rear brakes smoking

i have a 1998 durango with a 318 motor i changed everything on brake system proportioning valve master cylinder rotors brakes drums and still had brake fade and smoking in traffic only stop and go they smoked turns out i talked to an old school mechanic and he said it may be the brake line running along frame rail that is restricted so i looked under truck at line and it was severly rusted he said your peddal pushed puts lots of pressure on brakes to expand but when released only spring pressor returns shoes to normal because the line was so blocked it took a while for brakes to return resulting in brake fade and overheating smoking etc... and a rear ender in traffic from lak of braking like i had first accident in 18 years hope this helped at least 1 person