Problem with a Mechanic Shop

I have a 1990 Cadillac Seville. I had a mechanic shop do some work on the car, I wanted some new rims and tires for the car. They put 20 inch rims and tires on the car. When I took the car to them my engine had power and worked fine, when I got it back it had no power, it jerks when I accelerate and it has a loud rattling soung that wasn't there. They say I have a crank pully problem but deny that the rims and tires caused the problem. They also couldn't do the electrical work that I felt would help in assuring that the tires were height and width correct for the car. I looked on some tire web sites and the largest size shown to see was 18 inches for that car. I asked them to do a complete tune up and I don't believe they did. What does a complete tune up consist of and what machines do you need to do one? I asked for a new rear suspension, actually I asked them to remove the suspension that was on the car and put a regular suspension that allowed more height to the car for the bigger rims and tires I would have liked to have on the car, they couldn't do that. I would like to know if I just was ripped off and if you can provide me with other mechanics to talk to about my situation, before I seek legal help?