Right when I start third gear, on my TH700R4 auto, I hear a loud groan toward the rear of the car and the response is sluggish.

After a few seconds of acceleration, it seems to quiet down and the car starts responding better.

Does anyone know what would cause this?

I would like to get it fixed, but don't know if its the rear-end, tranny, etc.

FYI - I paid a mechanic, about a year or so ago, to rebuild my tranny. At the time, he claimed it was "tight" and that I needed to "put some miles on it". I have put many miles on it since then.
Don't know if this has any bearing, but I thought I would mention it.

Any info would be greatly appreciated.

Thanks!

 

Nothing in the rear end changes when the transmission shifts. It can be ruled out.

Sounds to me like 2nd gear isn't releasing, so it's in 2 gears at the same time. VERY VERY HARD on the parts that get subjected to this. However my memory of the clutches and power flow and hydraulic circuits in the 700 is a bit foggy, so I'm not positive what would cause it. Sounds rather like a valve body or separator plate type issue though.