Tony, make sure you get the correct load rated tyres, these cars take extra load. For yours it might be 97Y or XL, whatever they call them. Not all tyre shops will take care of this.
Also it may not be the tyres. Cars with other steering and suspension wear often feel good on new tyres, but as the tyre wears the underlying car problems become more noticeable again. Shocks, bushes all contribute, they gradually loosen up with age.