wheel problem ?

[krave]

I got a set of 20s with 275/45/20.But I'm having a problem when I get on the freeway I get a shake in the steering.I thought it was out of balance but the shop rechecked them and they came out ok.They said to have the alignment checked I'm having that done picking it up tomorrow but I'm not optamistic that the problem will be solved has any else had trouble getting the tires right or
has any thoughts on what else to check before I get even more pist off and take the rims back to the shop and run amuck?

Thanks