Problem with Overdrive

In my 94 3.4L, whenever I put it into overdrive and try accelerating above like 105-110 km/h, the engine moans and sounds like it's dying...then I put it into regular drive and accelerate and it sounds normal. When it's in overdrive though, it just sounds like something is powering down, if you can think to whatever sci-fi movie as a reference point. I'm not sure what to think of this-it's my first car, and for all I know this could be normal, but I doubt it.

Any input?

sure as hell sounds like a tranny or torque converter problem... i don't know much about auto trannies so i'm not sure what all is involved in overdrive...

So what kind of shop should I take it to just a general mechanic?

Is it red lining? Is the speedo and tach going down? I assume your still in WOT.

it may be a bad lockup clutch or related part. the converter only locks up in overdrive. So when it goes into overdrive, it may be engaging a failed lockup clutch. in any case, the dealership is the best place to take your car in my opinion. They have GM trained tranny specialists. Thats who i go to.

yea dealers are alot less likely to bs u on what is wrong with your car... seen too many average mechanics who just try to milk u for all of ur money w/out ever actually fixing anything...