I don't know how the gas tank on the 80 is but on other vehicles there is sometimes a mesh bag over the fuel pickup in the tank. This is (I guess) to keep the large crap from even getting picked up by the pump, so a pre-filter sortof. However, on several vehicles that mesh bag has been covered in gunk
I think it's more electrical since it runs fine and then all of a sudden is sporatic then can smooth back out , as long as i'm understanding correctly.
I've changed the prefilter/sock in my 80 and it was a piece of cake. If there's enough crud in there, it could be clogging it when the right amount of sloshing puts it in the wrong spot or rinses it to another spot. If you order the mesh part, also order the little rubber retainer thingy as well. It was a 2 banana job simply because of the safety aspects, and also the need to be extremely sanitary. Look for my post on replacing this a while back if interested - way back.