402 backfiring hard start

[1972_C20]

So, I've been browsing the forum and haven't seen anything about the issue I'm having. I have a 72 c20 with the 402. All stock minus an HEI. Truck was running and driving just fine. Drove it a good 30 miles for thanksgiving, left to head back home and it idled normal, but when I put a heavier load on it the carb began to backfire. I took it slow the rest of the way home. Went to start it the next day and nothing. Absolutely no fuel was pumping. Replaced fuel pump. Got it started and idles good, but as soon as I put the gas pedal down it backfires again and dies. Then it's hard to start. I've checked for vacuum leaks and can't find any. Pulled the cap off of the dizzy to see if there was moisture and it's dry. Starting to pull my hair out with this one. Any help is appreciated. Thanks.