what would cause my car to shudder pretty heavily between like 60-75 or mph? it starts just over 60 and then if you get it up to around 80 or so its smooth again. it shakes worse the less gas you give it, and seems to do it even worse in OD but i figure thats cause the revs drop even more then. but i dont know. it also suffers from a slight to moderate rough idle. but i never notice it when im driving, just when im sitting and even worse the hotter the engine gets.

check your coil pacs and spark plug wires

When the car is shaking can you feel it in the steering wheel (vibration or wondering)?
Can you still feel it while hard accelerating through the vibration zone?
Do you have any hills in your area you can take your foot off the gas and still gain speed? Good way to check wheel alignment, tires out of balance, steering issues etc.

Your rough idle may indicate a tune up and service? When was the last time your car had a tune up including plugs, wires, filters, o2 sensor, pcv etc.?

These are tricky problems. Pdad is on the right track here. Try swapping front tires to the rear and rule them out. See if it does it hot or cold or both (engine temp). Do a full tuneup if it'* been awhile like he mentioned. This could be ignition or suspension. It'* just gonna take some patience to get it narrowed down.

no you cant feel it if your hard on the pedal through that speed, its just when you let off the gas. or if your accelerating slowly or whatnot. last tuneup? lord knows when i need one bad i know, i plan on just changing out the basics on the next oil change. like air filter, fuel filter, plugs/wires, and see if that helps. but anyway the vibration seems to stay the same regardless of uphill or downhill, sometimes a bit worse downhill. i dont have the time or the money or extra car to put it in the shop or do it myself right now, but school will be out soon...thanks for the advice as usual. i hope its not suspension related cause usually thats expensive.

check for tire cupping and for pot-hole damage to radial core of the tires. I went through this last year and was caused by bad struts. Also check for tire balance

i was just wondering how much this would cost if i brought this in to be done this summer? would it be cheaper if i bought the stuff then had them do it? thanks

sorry to get off topic

Rotate the tires as WIllwren suggests that costs nothing as you can do it your self.
Your tires maybe out of balance, rotating them will give the car a new vibration?

If you have some common tools you can perform a tuneup your self, most shops dont like to use 'others' parts as there is a markup on 'their' parts and they lose money.
The tune would run over $300 with parts and labour.

This is textbook balance issue. In the shop, this would be first thing I would do. Any time anyone came in with a shake at 110kph (65 mph) the lights went off. Especially if it went away after about 125-130kph(85mph). But absolutely do the tune-up. It is money in the bank as far as I am concerned.

thanks for all the input, tires will get balanced very soon, right after we get our truck fixed.....stupid Ford..... but ill definetely do a partial tune-up when school gets out, like at least plugs/wires and filters.