Ok my Park Ave has a very slight vibration and I have done the following:
Rotors all 4 new AC Delco'*
new rear air shocks
New rim to replace bent rim
4 new Goodyear Comfort treads all balanced
new AC Delco wires
new AC delco iradium plugs

Vibration is MUCH better but still at 65 to 70 there is a slight vibration felt thru the floor and seen in the passenger seat head rest. It has 100k miles should it ride glass smooth ?

Also air pressure is 35 cold, should it be 32 cold for a better feel ??

Maybe Im asking too much

I have the same problem, first I thought it was shocks, then tires (new w/ balancing and everything), and these helped but still has slight vibration around 70ish. I've just learned to live with it. You covered everything I would have suggested. Maybe someone else can give some other ideas.

There should not be a vibration that causes the headrest to vibrate. The first suspect is a tire out of balance. But with new tires you should be good if they did the job well. Worn bearings or joints can cause the same problem, e.g., tie rod ends inner or outer, ball joints, bad struts, bad strut bearings, bad wheel bearing, worn control arm bushings. And, it is important that the mating surfaces of the wheel and the rotor are clean and smooth and that the lug nuts are tightened evenly. This is often neglected and results in warped rotors and vibrations at speed. A bad drive axle can also cause vibration, but it is very rare.

For safety'* sake, you may want to make sure all your suspension parts are safe and tight.

I had an Olds Ciera that acted like yours. Never found the problem, but, It got better with time, and eventually disappeared. Maybe you will be so lucky.

If it will help any, there is the rule of thumb that, "If you feel the vibration in the steering wheel, it is in the front. If you feel it in the seat of your pants or floorboard it is in the rear."

So, yes, rear wheel bearings.
Or have a different shop re-check the balance on your rear tires. It could be one shop'* machine or tech. Even putting the weight in a different location (inside/outside/center of rim) can make a difference. But the balance machine will tell the shop which one is needed. You shouldn't have to guess at that. They can also check for roundness, etc. Always good to get a (cheap) 2nd opinion on the balance, etc.

Oh, and your air pressure should be checked w/tires warm. Pressure rises 2-5 lb. with warm up. Door sticker should list pressure. I try to run mine at 32 warm. Of course, harder tires will get better gas mileage, but will ride rougher and can wear out the center tread early if too drastic.

I took it back to the tire shop today. 2 of the 4 new Goodyear Comfort treads had a slight hop, he is getting me 2 new ones. These are only a week old !
Rotors again were AC Delcos and I cleaned them with brake cleaner real good and cleaned the mating surfaces down with scotch brite wheel on the hubs.

Again the headrest vibs a little at idle in park but not in drive. I cleaned the MAF and throttle body. Motor and tranny mount bolts are tight and not much movement from the motor putting it in gear w/ foot on brake.

I dont mind the vib in park but the one felt at 65-75 I do mind.Again maybe I am expecting too much. Different brand of tires help ?? My Bonnie had a similar problem too. Maybe its me

I am hoping these 2 replacement tires take the problem away for good. Its not bad just drives me nuts ! Slight vib felt in floor and seat. You can feel a little in the wheel but NO movement. No noise from wheel bearings.

Tie rods and ball joints are tight.
I really dont want to go just dumping money for something that may never go away.

well they replaced the 2 rear tires and balanced them and its the same....I wish I could remember 100% if it did it BEFORE they replace the torque convertor but it doesn't matter if its in netural or drive it still does it.

Its not terrible but this car should ride like glass ! Again you can kinda feel it in the wheel but not see it but see it in the armrest and headrest on passengers side and feel it slightly in the floor.

The tires have 32 psi in them. I cant believe it owuld be a wheel bearing as they are stone quiet, also cv shafts dont sem likely,,,,,
Open to ideas

Not to go off crazy on something, but have you considered an ignition miss?
I went through something sort of similar. Of course, mine would cut out on hard acceleration and the engine would shudder in OD if I tried increasing speed too quickly
Then it started missing in Park (just a vibration and spitting at the exhaust at idle), I finally found the culprit. I had at least one coil die and another almost simultaneously. Was going to say something before, but don't want to shot gun the thing.

If you want to try it, I can send you a quick check from the FSM. But it only is for a miss at idle.

sure I will try anything. It doesnt ever miss or skip and NO check engine light either. Plugs all seemed lite tan color and you couldn't tell one from another??

Again maybe im being too fusy but its got to be something. I hate just throwing money at things unless I am pretty sure. The plugs,wires and rotors were all orignal and ith 100k it was due so I dont consider that wasted money.

The tires were replaced free. I still feel tires maybe or something when the tranny was removed........

Only because of the vibration in Park at idle... here it is, a cut and paste from my post.

Start engine; allow to stabilize; unplug IAC motor (not to exceed 2 min.); use insulated pliers (AND a rubber glove is great too); (at the coils)pull one plug wire at a time while listening for miss (in your case vibration) to get worse or stay the same. If it gets worse, that cylinder is NOT the problem. If it does NOT CHANGE, that cylinder or coil IS the problem. Of course, replug the wire and go to the next one, etc.

Observation: If it is a coil .. The Bad side of the coil would NOT arc over to coil body when one wire was pulled. But the good side WOULD arc back to the coil body with the other wire off. Hope that makes sense.

This is a quick, even better, FREE, check to eliminate bad ignition on a cylinder. Who knows??? ...

your plight touched a nerve. i am also someone who might be called overly sensitive to any vibration in a car. for years i went thru the bent rim explaination, a drive shaft out of balance, out of round tires, improper torqueing of lug nuts, poor quality rotors---well you get the idea. i do not disagree with any advice given regarding your problem and it may well turn out to be one of those very things. but, since you are looking for any thoughts on the subject, here is my story.

i have not found any tire except michelin that is capable of being balance to my satisfaction and more than once i have had to return to the business that balanced the michelin and ask them to try again. and to my great pleasure, eventually i could get a balance that would allow the car to run smoothly. for the record i have had more problems with goodyear tires than any other. i am a 73 year old driver so you can imagine how many miles go into this reply. sorry for the lengthy discussion but i wanted you to know that you are not alone.