I have a 2002 5.3 Silverado 4WD with 33K miles. I have noticed a "shudder" or "shimmy" when the truck shifts from 1st to 2nd gear. It is most noticeable around 15mph. Sometimes it is hardly noticeable, and other times it is fairly obvious. I haven't noticed any patterns that dictate when this will occur. Can someone tell me what this is?

I'd suggest that you get it back to the dealer you bought it at before your warranty runs out! Let them worry about it!

If that shudder or shimmy is a vibration, I'd probably say it sounds like a torque converter going down. Either way, you need to get it back to a dealer and let your warranty pay for it.

A coworker of mine had the same problem which turned out to be the tc going bad. Because it didn't do it all the time the computer wouldn't pick up on it and if it did it would clear on a restart so the scantool wouldn't see any codes.