Breaks

I am working on a 1997 ford F-150. The front right break keeps locking up. The caliper has been replaced, the pads replaced, I have also bleed the lines completely. I don't think it could be the master cylinder as the left break works fine. I am kind of stumped, any suggestions would be greatly appreciated.

Some times the hoses collapse internally holding pressure. I would try this first before doing a rebuilt master cylinder.

The front right break keeps locking up. The caliper has been replaced,.
The above suggestion about the hose is valid, but I have found your problem is more commonly due to a defective caliper.
Typically, inexpensive "new" calipers for older vehicles are usually rebuilt used cores. Usually this is fine but once in a while you will get a defective rebuild.
Either the piston or bore is contaminated/rusty or the O-ring around the piston was improperly installed. Usually parts retailers will happily exchange a defective caliper for another one.

I'd check to ensure the sliders are greased properly. I've also seen more collapsed hoses than i have defective parts, but its always a possibility.