Front Brake Locked Up!

[dnights]

So I am still new to this area but I have had my 81 Chevy C10 Longbed for over three years now and its been a real trooper but starting to have problems.

Just over a year ago I started having issues with the front brakes locking up or pulling to one side when the brakes were applied so I went ahead and got new calipers (which was a headache) and new pads. Well that temporarily solved the problem. My father-in-law has been driving it since I moved and since the weather got extreme hot and no ac, he went back to driving his truck. He has been starting it and making sure it still fires up but he actually tried moving it the other day and the front brakes are completely locked up. I am actually lost on what to do to fix it this time. Anyone has some ideas on what to try first.