What is the presures when the truck is turned off and what is the presures right before the compressor kicks off? It is still posable there is a clog somewhere. There is a way to jump out the low and high presure switches. You should try that and see if it stays on. If it is a clog and the high presure switch is cutting it off dont let it run too long because it could blow out o-rings hoses or any number of things.