Sounds like a fuel/fuel delivery issue either the fuel PSI is low coming out of the Vaporizor(should be about 4.5 PSI) and it is starving for fuel or the injector is acting up and needs replaced....might also be the fuel PSI sensor next to the injector.....another possibility is the Lockoff...it has a small screen filter in it,possible that is getting plugged,or the Lockoff itself is acting up and shutting the fuel on and off,never run into that tho on this truck..