Truck drifting to left

[sagebel]

I have had my leveling kit on for almost two years. About four months ago it started drifting to the left. If I hold the steering wheel centered the truck drives straight. When I let go of the steering wheel the truck drifts to the left even on heavily crowned roads. I put the stock tires and wheels back on today and the truck handles the same. Alignment shop has aligned the truck to factory specs (recommended by Ready Lift). Any ideas?

[sagebel]

Update for future searchers. Looks like the left wheel bearing is shot. No play when you check by moving the tire back and forth but I can move the u-joint inside the knuckle back and forth with no problem.

[sagebel]

Ford says wheel bearing is fine and they agree that it pulls to the left but have no idea why.