Transmission or???

I have a 2000 Chevy Monte Carlo SS equipped with 3.8L V6. I have had this recurring problem that my dealer doesn't seem to diagnose properly...

When accelerating, the car seems to accelerate fine until about third or fourth gear. Then, the car will shift, but the car revs and bucks...If I really press on the gas and get the RPMs up to 3000 or so, the problem goes away. Also, this only happens when the car hasn't warmed up completely. Once the car is up to full operating temperature, this does problem does not happen. The dealer replaced a throttle position sensor, but it didn't seem to do the trick. They insist that if this didn't work, then the transmission would need to be replaced? Are they right? And since this didn't work, I am pretty skeptical about anything that they say.

Has this happened to anyone else? What could the problem be? This car has been well-maintained since I bought it, and it only has 67,000 miles on it.

Thanks!

There is a known issue called "chuggle" or "fishbite" on the GM 4T-65E transaxle used in w-bodies. I will see if I can find a thread regarding this issue and post a link.

here's a link to one thread that I feel addresses the issue the best.

http://www.automotiveforums.com/vbulletin/showthread.php?t=517684&highlight=fishbite

I hope this helps

Thanks... I have an appointment scheduled for tomorrow for service on it. I will relay this to the tech to see if any of this could be the problem. I'll post as soon as I find out.

I appreciate your help!

The dealer said it was the pressure control solenoid. With this part, transmission flush, new spark plugs and tune up, I am set back $1000. Hopefully this solves all these problems.