I would sanity check all the clearences at full lock either side, make sure your not rubbin. All your tires the same? my girlfriends elcamino did this when i got a flat and swapped on the fullsize spare just beacause the treads/psi rateing where different. Front right on the outside, driverside on the inside. Felt straight too untill you get over 25 or 30, let go and not touch it it would pull ever so slightly to the right. Most likely something misalighed (hopefully not bent).