Slant won't drive over 25mph without cutting out

Had something similar on my mom's old 84 5th avenue
It ended up being a plugged sock in the tank.

A neighbor has a 70 f100 that his dad bought new. Had a similar issue twice. First time was a collapsing rubber line right off the tank, (which was original from when the truck was New) the 2nd time was a condenser gone bad
On my old 79 D100 I had it do something really weird (and this one was a /6 besides)
Back when I still lived at home with mom and dad, I came home from work and hit the shower. It ran great on the way to work and again when I went home at the end of the day. Went in the house took my shower and went to leave. It wouldn't fire, crank and crank and crank. I burnt up a starter trying to figure it out.
When I went to hook up the battery and try it again, it was about 1/2 dark. I cranked it with the hood still up and then I saw it. A huge arc from the coil wire (about midway along it's length) to of all things a heater hose, also about the middle of the hose. . I couldn't believe it. Still have a hard time understanding that one 30 years later.
I moved the coil wire over a couple of inches away from the hose and the damn thing fired right up and only had to crank over a couple of revs and it was running.
A few other things for you to check.