2001 diesel 703 cold start

2001 diesel 703 cold start, i,ve had this truck for over a year now, i'ts been in three diffrent shops for at leaset 3 months. no one can find whats wrong with it,changed every part you can name, it will not start when it cools down, now you can plug it in get some temp up, starts and runs great,but dont go to a meeting somewhere for 3 or 4 hrs or you'll need a ride home.glow pugs new and good, compression on 2 cylenders are 350 and 360 the other 4 are great. according to all thats worked on it it should start.help please