If its a 2wd, the "bending" will work, but not a 4wd. If your wheels are bowing in, they may not have done the lift properly. I've done a couple of these. The F150 and F250 are the same except the 250 has leafs and the 150 has coils and radius arms. The rest is the same.
Since they lifted it 4", can you tell if they put in drop brackets for the axles? These are brackets that bolt to the engine crossmember, and are the pivot-point of the axle beam. Any lift kit over 2" comes with these brackets to drop the pivot point down, and keep the same suspension geometry. You have to use them.
Sometimes people will use only the springs to lift the front of these trucks, not use the drop-down pivot brackets, and think they can just have the camber aligned that way. That's not the case. That causes the bowing you describe. A small amount of lift can be adjusted for by your camber adjusters, but 4 inches is a little much.
Also, but I doubt this is it, Check the condition of the bushings the axles where they bolt into the brackets.
I would take the lift out, and put it back to stock.