Drive shaft repair, not happy about it.

I have got a question for all you mechanically minded and auto techs out there.

Recently I noticed a slight vibration upon accelleration of my 04 Chevy Avalanche with about 90K miles. It was slight at 25-30 mph, then quited down til around 65+ mph. It felt drive line to me. Mostly because when I took my foot off the gas pedal, the vibration went away.

Dealer replaced the U joints at a cost of $400. Problem went away but after about 100 miles it came back, exactly as before. Took it back to them and they fixed it free, saying one of the U joints was bad. Hmmmmm.

Well the car drove fine til I hit about 100mi. again, and the exact same problem occured. Took it back, this time asking to speak with the Svc Mgr. He assured me he would find the problem and stating very cocky like, " never had a vehicle we coulndt fix". Sounds good to me.

Well his final diagnosis was the drive line was fine, but I had cupped tires. And that was the cause. I could drive the vehicle all I wanted with the tires that way and would not damage the vehicle.

I gotta say, deep down it all sounded like a big hanny. I am not an expert or tech, but common sense was saying BS.

A couple weeks go by and I cant stand the vibration. So I take it to Dealer #2. Service tech jumps behind the wheel with me and we test drive it. I ask him if he feels what I am talking about and he says OH yea, it feels drive line.

Bottom line is, the drive shaft was bent. Need replacing and had them do the repair. Have put about 5K miles on it and it drives great.

The tech told me if I continued to drive it with the bent shaft, It could of cost me a lot more to fix because it would damaged bearings or seals or something in the trans and/or rear end.

My Q is, was the bent shaft wearing out the U joints? and Dealer 1 just messed up, or could the drive shaft been straight all along at dealer 1, but somehow was bent after the third time they tried to fix it. ??? Would like to know your thoughts cuz I am thinking of going to dealer 1 and asking for some sort of refund. ( pipe dream I know ).

Thanks