The brake pedal turns rock hard after the truck warms up, and strange odor appears from the brakes. Brakes lock up! Please Help! Mechanic is puzzled!

2WD or 4WD? Seems like yer brakes are stuck and are overheating...hence the funny smell. I'm guessing it's a pretty sharp odor? How many miles do you have on the truck? What other maintenance has been performed on the brakes? What mechanic are you using? This is a basic brake problem and he/she should've diagnosed it properly. You might want to look fer a new mechanic. :(

What tests have been performed on yer brakes? How good are the calipers? Have they been inspected fer sticking? If yer T-100 is a 2WD, how good are the guide pins? If the rubber boots have been compromised, water will rust the guide pins and could keep the brake pads from retracting. Have the flexible brake lines going to the calipers been replaced? Old flexible brake lines can act as a one-way valve and keep pressure on the pads after you let up off the pedal. Replacement of the flexible lines are the only way to fix that problem.