Has anyone else had problems with Discount Tire's free balance and rotation?

I put 18's on my 04 Celica and eventually took them off after a while due to shaking in the steering wheel, especially when on the highway. I went back to the stock 15's and the steering wheel shaking has gone away but it seems like the car is a little bouncy when driving and that it isn't handling 100%. This weekend I'm thinking of going to Firestone and paying $60 to have them to do a lifetime balance and rotation since they just started to offer it and I'm having no luck with Discount Tire. I already have a lifetime alignment with Firestone for my car. I'm also very obsessive about how my car handles. I've driven other people's cars and I don't notice the same problems. Does anyone have anything to add? Thank you.|||No problems to speak of, but it sounds like your tires are over-inflated. If they're really low profile, that may be to save your wheels from getting bent rims. Most plus-ups like that require higher pressures to keep from ruining those expensive rims.