Whats up guys, have a 2000 NB that I recently got some new tires for. (Kumho Ecsta AST in 205/50/15). When I have driving over 40 mph and or on the freeway the car doesn't drive straight...it wanders to the left and right. Also when I give the car some throttle it pulls to the left and when I let off the gas it pulls to the right.

I recently had an alignment and havent hit any potholes/major bumps so I think that is still good. I checked the PSI on all tires and all 3 are 35 psi but the driver's side rear is at 9.5 psi. Is this the culprit? I realize I may have a nail in the tire but my question is this what is causing the car to not drive straight?