Transmission Shudder problems of the 2001 Chevrolet C2500

I just bought a used 2001 chevy silverado on 1/29/09 k2500 the abs lights keep coming on and now my transmission is slipping or something when I get up to 65 mph the truck starts vibrating and the transmission makes a loud clunk noise I only had the truck for a day then had to bring it back to have the knock sensor and the rattling noise checked they told me it was a hub that I had to pay for after they gave me a work order that was suppose to be fixed also the check engine light keeps coming on and they said that was also the knock sensor and said it was replaced but ten minutes after they fixed it the check engine light was on and the truck has been leaking oil that they said was fixed I would like help to see if I can get these problems fixed or my money back thank you.