I having a problem with stalling When the truck.

I having a problem with stalling When the truck is warm and at idle( lights, stop signs. Ect. ) Took the truck to the local shop. They cleaned the throttle body and performed an adaptive memory clear/reset. They finally told me that the problem is to intermittent to diagnose. Today I got off they highway the truck was fine. I then filled the tank, when I went to leave the truck stalled out several times. After 8 hours of work drove home, got off the highway experienced no problems at all. Could this be fuel problem? Or possibly an intake gasket gone bad? ( I am tempted to replace the fuel pump) Truck has had a tune up recently also. Do you think I should get a second opinion from a another shop? Not sure what to do now? Thanks for your help!