Weird alignment issue

So I took my 06 prerunner in to have it aligned; I have stock struts with camburg spindles and a 1" block in the rear sitting on 285/75/16. Alignment is done with no issue and the truck drove great for one day, hit a pot hole and then the steering wheel started to sit slightly off center while driving straight. No obvious pulling to either side. I took the truck back and the mech. fixed it real fast and apologized, stated that he rechecked all the bolts and everything is tight. Fast forward to one more day and the truck has reverted BACK to the steering wheel being just off center. This time the truck also seems to turn a bit easier in one direction than the other (No pot holes this time). Any idea what could be causing this? absolutely nothing has changed on the truck over the course of one day and the alignment was perfect after the mechanic fixed it the first time.
Thanks for any input

 

Thats pretty strange, maybe its in the rear end? Are your u-bolts all tight? Blocks haven't shifted....?