On cold starts, my Acura TL 3.2 Type -S with 252k miles slips when put into reverse. If I shift through other gears and back a few times it may catch, or if given throttle while sitting in R, it shits very hard with a big thud. What could be wrong? No slipping in other gears, and the fluid level is fine. The transmission was rebuilt about 8-9 years ago., and this has been an issue for about 4 years now.

 

Sounds like a failing torque converter. if you give it gas, it produces more hydraulic pressure via the engine/converter spinning faster. Is there any whine present? these things creep up very subtlety.

It could also be the ATF temp sensor; as that's listed to cause late shift into R per the service manual and that is something that ties into your "when cold" description...

Hard to say without more details.

Here's one of my favorite transmission related videos; it shows what the failing torque converter sounds like.

 

No whine, no code P0710 for temp senor failure. what additional details can I get you? I'm getting the car from son today and have a chance to run over it with some checks. Running fine in all gears after it warms up. On cold startup, running through all gears seems to help R engage quicker.

 

Are the temp sensor, and clutch pressure control solenoids OEM? If not; they may produce a non-oem range response when things are cold that is giving you your problems.

 

I can't confirm that but, I trust the mech that worked on it. He