Need a brake expert

[mybigtruck]

I have been using Search function but nothing I find seems exactly like my problem. Truck is a k10 that has had K20 running gear installed and this just started. Brakes are vacuum boosted power brakes. Problem is: Drive approximately 8 miles on freeway. Truck becomes increasingly sluggish, finally pull over and Rt front brake is smoking. Brake pedal rock hard. Wait approximately 45-60 minutes problem clears and truck drives fine. Drive on surface streets and some freeway approximately 25-30 miles no trouble. Next day drive approximately 9 miles on freeway. Truck becomes sluggish and brake pedal gets rock hard again. Wait 45 minutes and problem cleared. This truck has: New (re-man) calipers, new front brake hoses, new master cylinder and vacuum booster. Any ideas, suggestions opinions?