Chev engines mount with the arm up while gmc engines mount with the arm down, or something like that...
Throw one of those disposable filters inline below the tank, that will tell you for sure if its having problems from the tank. As soon as it dies, climb under and if the filters dry youve got crap in your tank.
Other then that Id try cleaning the carb out. You would be so surprised to know what a speck of gunk can do inside that carb. I had issues with the jet being plugged on several of my trucks. Just enough to let it run fine parked, as soon as it was driven itd stumble. Just cleaned out another carb that ran for 5-10 minutes before dieing, runs fine now.
Good luck. Jeff
