When I first bought my rodeo I got new tires and had it aligned and it does the same thing on grooved highways, follows the grooves. I think it might need more toe in. I know there is a bulletin (IB00-06-S001) for '98-00 Rodeos with a change in the alignment specs. It changed from 0mm-(+/-)2mm to 0mm-(+)2mm. So apparently they dont want any toe out, only toe in up to 2mm. Maybe whoever did yours didnt look at the updated specs.

I'm starting to get used to it but will get it aligned again once I get the 'pop' noise in front figured out and fixed. Hopefully they can get rid of the problem.