Truck won't stay running after new gas tank installed

[1979 GMC Sierra]

Hey guys, i got a new gas tank put in the other day cause my old one was leaking. After it was instealled, i drove the truck home from the shop (15 min drive). The truck then sat for 2 days. Then, when i went to start it, she started and ran for about 30 seconds and then shut off abruptly...like it was out of gas. But there's gas in the tank. I kept starting it, with the same thing...shutting off after 30 seconds. We figured the new gas and vent hoses put on the tank might be a bit too long and were kinked...so we lowered the tank and cut the hoses to make them shorter and stop any kinks. Brought the gas tank back up and started the truck...but the same thing still happens...runs for 30 seconds and shuts off. I can't figure out what is wrong...do you guys have any ideas ? The truck ran fine before i got the new tank put in...so this is weird and frusterating.

Travis