about 10k ago I lowered my 150 using the mcglaughlin springs (2/3). I had it realigned and now front tires are wearing off the inside edge very bad. Is it impossible to have a correct alignment after lowering or just a bad job by the shop?

 

Or you could have knocked it out sometime.

 

camber was off according to the shop

 

yah its hard to align a lowered truck correctly. My best advice is tell them to do camber and toe and not to worry about caster. Caster may lead to a slight pull in the steering wheel, but will not affect tire wear if it is not within specs.