I recently had my transmission with a used unit. The shop said it was a GM rebuilt unit and they put new fluid and filters in it. My problem is this, the transmission seems to work properly shifting through all the gears and it has no slippage but sometimes the overdrive doesn't work.

I try stepping on the gas, downshifting than putting it back into overdrive but nothing works to get it to go into overdrive. If I pull over and shut the car off it will start working again. It seems to work fine when it works.

The transmission shop just changed the filter and fluid again and they said they cleaned up all the electrical connectors but it started happening again yesterday.

Any ideas what might be the problem?
I never had this problem with my old unit before it went out.

Something similar to that happened on my '93 SSEi. In my case, it tripped an error code in the ECM, and the problem was the TCC (torque converter clutch) solenoid.

Rather than having the transmission shop rebuild the transmission, I opted for the better 50,000 mile warranty that comes with the rebuilt GM SRTA unit, and I had them install that. There haven't been any problems with the rebuilt transmission.

If yours has a problem at the electrical connector, they should diagnose and fix it, otherwise there'* a problem inside the transmission, and it should be covered by your warranty.

Good luck.

I just had my TCC solenoid replaced. I had a problem where mine would shift into overdrive sometimes, but other times it wouldn't. The code displayed was the TCC, and having it replaced has fixed the problem. Its a little expensive, and its better to have both solenoids replaced while inside the trans., because its incredibly difficult to get to. I took my car to Bil and Earls, in Baltimore Maryland. They charged $600.00 for the replacement of both solenoids. You would just have to decide if its worth it. Of course it was in my case, because the trans. was a little over a year old