Ok my 3800 engine (1997 PA) is mated to automatic 4 speed 4T65-E
Had filter & fresh fluid done a few weeks ago. Only had this car for 2 months.
Has 84 k miles on it now.
Had no problems driving 10 hours return in the mountains with cruise on....
But...in city driving once it gets real hot am experiencing hard shifts from 1-2-3
etc. Can sometimes shut car off and then problem seems to go a way. If it is cooled down no problems.
Called tranny shop and they said to get codes read, ( i have no engine lights or nothing on) and they stated that the valve body can get sticky and one valve may not be opening properly so computer adjusts for a higher pressure and that then can cause the harder shifts. $1600 quoted for new valve body with all new electronics, up to $2500 if it needs clutches etc.
Any input appreciated.
Anyone got a link to rebuild manual for this transmission?

You most likely need a pressure control solenoid. If you scan the car with a quality scan tool, it will probably show a P1811, which will not turn the light on.

Check in the tech info area about installing a shift kit in a 4t65e. It will help you remove and clean up the shift accumulator. Sometimes these stick and give harsh shift.

Thanks Steve & Dan for that info.
I guess I am being told that the valve body is on the side therefore the tranny has to be removed. How difficult is it to remove it? Hours? Any links again?

I can have a trans on the floor next to the car in about 2.5 hours. If you've never done it, figure 6 hours. You need to drop the sub frame and support the engine from above.

You do not have to remove the trans to remove the valve body. You will have to remove the subframe and the side cover.

Thanks Dan, Glad to hear hear you can have it on the floor in 2.5..GM'* book was 10 hours x $125 per hour LOL!!!!! How long to just drop subframe?

And Steve Thanks for the info on not having to remove tranny to access the valve body.

Where is the shift accumulator located? How much $ are they?
Also wonder what shift kit is worth and how hard to install??

Also Steve where is the pressure solenoid located? $? THX!
I need some diagrams to look at.
I would kill for a FSM right about now.

Here'* how you make a shift kit, save your money and make it yourself.
https://www.gmforum.com/performance-137/making-installing-shift-kit-4t65-hd-transmission-278802/

Dropping the sub frame isn't to hard if you have a shop. Jack up the car as high as possible, support the car so the sub frame is free. Use long 2x4 and jack stands. Remove front wheels, undo the lower control arm ball joints. Remove axle on drivers side. Make sure all wire clips are removed from sub frame. Support engine from above with chain and a 4x4. Unbolt motor mounts on sub frame. Remove 2 bolts on steering rack, attack steering rack to exhaust manifold so it don't fall down. Remove power steering lines that are mounted to sub frame. Support with jacks. Remove bolts holding frame to car, then lower. Make sure you didn't miss any wires or pipes like transmission cooling lines. Make good time and you can have the SF out in about a hour.

You can then lower just the drivers side using a jack. It'* very tight with the brake lines. When just low enough, you can remove the side pan. The EPC solenoid is in there. I've done a few like this. The EPC is the big one on the front side of the valve body. You need a hook to pull out a clip, and it pulls right out, put new EPC in, replace clip and plug it in. Put side pan back on, torque to 18 foot pounds.

Well I just got the 4t65E on PA scanned at trans shop. Info from them as below.

P1604 loss of IPC serial data.
P1641
P1654 (FC Relay Control?)
P1811 maximum adapt + long shift

They recommend pulling the trans and install new Sonics valve body with updates and stainless valves ( has new pressure Solenoid in it) etc.
They would also inspect clutch bands etc on bench and advise if $$$$+++

Any thoughts on above codes where do I start ????