RPM doesn't decline when I stop pressing gas pedal
 

I bought a 944 for one of my kids (87, 944, automatic) a while ago. The timing belt broke and I got the head rebuilt and belts replaced. Ever since that happened the RPMs run high on the car, about 3,600 at 70mph and they don't lower when I stop pressing the gas pedal.
I'm at my wits end with this. I have called 2 Porsche dealerships and asked them along with several reputable mechanics and all of them act like I'm insane. Does anyone know what the heck is going on with this car?

Take it to the dealership and or shops and show them what it is doing. Most will do it free if you come in and act like your on your way to work or to a BIG event for a family member. Just ask them to check it out so you have an idea on what to replace.

That is the best advice I have, maybe a more senior member can chime in

the rpms won't go lower when you let off the gas, as in the throttle is sticking?

does it exhibit this behavior when car is parked in neutral and you just blip the throttle? might wanna pop the hood and blip the throttle by hand.

Thank you for the responses.
I would like to rephrase. Upon reaching highway speed, 65mph, automatic transmissions allow the engine speed to drop back into a cruising speed. 2300rpm. Is there a vacuum line on the Porsche transmission or an electronic control that will allow this to happen?
Note: transmission shifts perfect 1st, 2nd and 3rd gear.

ahhh yer saying it doesn't shift into overdrive?

my 87 na 5 speed did this a couple times, cable was catching on a rubber hose on the engine. also look under the foot feed pedal, esp the floor mats

I think he's trying to say it doesn't shift into the last gear. Usually when you let off the gas on the highway, the car will up shift and the rpms will drop. I'm not sure how the 944 automatic transmission work, but maybe check the transmission fluid level? I know with hondas/acuras, if the transmission fluid is low, it will shift very late. Or maybe there are vacuum lines that control the shifting?

is there another shift position, or does the cable need adjusting so it goes into OD?

according to clarks garage, it says it can either be low ATF, stuck main pressure control valve, or internal transmission problems.