Help! have a Guatemalan doctor friend who travels around the country doing free clincs for folks all over the country. Most travel is in U.S. build GMC/Chevy Suburbans - K1500 w/4WD. This one has 5.7 V8 - gas powered. Recently started this annoying trend. Fill up with gas. Runs perfectly. Allow tank to get to 1/2 full. Vehicle quits abruptly. Wait a few minutes. Starts right up and drive fine for 10-20 miles. Abruptly quits again. Does this routine until reaching a gas station and filling up again. Somewhat dangerous in that travel is often in difficult terrain and gas stations are few and far between. Hoses, lines and pressures have been tested. New fuel pumps (2) have been installed. All to no avail 
Out of ideas. This chump has been stumped!
If he immediately takes the gas cap off, does it solve the problem? If so, something’s wrong with the evap. control system.
I’ll have him try it!