Could be a bent wheel, perhaps - especially if it's a continual feel of something being wrong/out of balance (versus only occurring at a specific speed). Could be a bent axle/wheel spindle. Also could be a flat spot in a tire from it sitting in one place for a long period of time.
But if the dealer says they changed the tires, I'd think they would have changed the tires and wheels as an assembly. So that should rule out the problem being with a tire or wheel.
Bill
