Chevrolet Repair: Engine stalls under load, altitude 5000, fuel starvation

Question
I have a 1981 GMC 250 straight 6 with a Rochester Varajet 2se carb installed in an old landcruiser. Fuel tank has been refurbished, new filter and mechanical fuel pump installed. Engine starts and idles fine but when I put it into gear and start driving down the street I get about 200 feet in 1st or possibly into second gear and then it sputters and stalls out. I checked the carb and it appears that fuel is still flowing in (maybe not enough? Not sure how to check that). I have checked the timing and it is set at 10 degrees BTDC. I am at higher altitude (5000 feet should it be more/less?). I may be wrong but the spec sheet I uploaded called for that. I'm trying to narrow this down rather than going to buy a new distributor, rotor, cap, coil, vacuum advance, and/or carburetor.
Any ideas on where to start would be greatly appreciated.

Answer
HI KENDALL,THE ONLY WAY TO FIND THIS IS GOING TO BE WHEN IT STALLS OUT LIKE THIS,CK TO SEE IF THERE IS ANY FUEL IN THE CARB. WHICH IT SOUNDS LIKE YOU TRIED THIS.NEXT TIME THIS HAPPENS,BRING A CAN OF STARTING FLUID WITH YOU,WHEN IT HAPPENS SPRAY SOME DOWN THE CARB AND IF IT STARTS WE KNOW IT IS A FUEL STARVATION PROBLEM.THIS SOUNDS LI9KE A FUEL PROBLEM...DOES IT RESTART AFTER A WHILE OR NOT ???
GET BACK TO ME WITH MORE INFO.TOM..