Brakes Locking up

4 yrs. Ago the front brakes locked up. They were cherry red, hot and literally smoking. This resulted in the installation of new rotors, new calipers, new brake pads, new brake hoses, all new brake fluid, new seals and repack the bearings, etc.
Than in March of 2008 I had brake problems again which resluted in 2 new brake rotors, all new brakes pads, repacking the hubs and new seals.
The first brake job was wround $1,000 and the second one was approx. $500.00.
At 151,000 miles (fall 2007) I had two new tires installed on the front and new two tires on the rear. I kept the best tires from the old tires and installed them on the rear inside of the dual wheels.
At 174,000 miles I purchased 2 more tires, installed them on the front and placed other two on the rear.
All total, the rear tires have about 23,000 miles; the front tires are brand new.
Just two weeks ago I was driving my truck and I noticed that the truck pulled to the left when braking and pulled to the right when driving. The front end wouldstart shaking so badly that I could hardly hang onto the wheel.
I went back to where I had the tires installed and had them check for balancing and a defective tire. Everything checked out. I drove about 20 miles and found the tires to be extremely hot and the rims would have blistered your hands! I took it to a mechanic and they told me that the caliper is frozen up on the right side, the pads are totally worn out and that they need to replace the rotors and brake lines and so forth.
So for the third time I have same thing ocurring again - this time only on the right front (although I expect it's just a matter of time before the left side fails as well). My quote is again, around $500.00 but only for the one side! This quote is for new rotor, calipers, repacking and so forth.
My question is this - before I spend good money after bad (Obviously as this is occuring again!) - What is causing this brake failure? What are the mechanics missing? Something is being missed or else this would not keep ocurring.
My truck is a F350 Heavy Duty with a diesel engine, manual transmission, crew cab, long bed and has about 174,000 miles. It is driven for pleasure (on week ends) and I do use it to pull my horse trailer. As you can see, I have only put 23,000 miles on the truck since March of 2007 therefore it would not be excessive mileage and/or wear.
Right now my turck is sitting until I can find out the cause. No one seems to have a single clue. HELP!