Hi y'all been searching here and other forums. Replaced fuel pump and sending unit on 03 pathfinder (gauge was pegged past full) now gauge is still pegged when truck is running but when turned off the gas gauge reads where the feul level is in tank. Turn engine on and it pegs again. Would this be a ground on the tank? Or short going to gauge cluster?

I doubt it's a bad tank ground, the fuel level is a simple balance circuit that won't change reading between running and stopped. What complicates this is the fact that it reads correctly when there's no ignition power to the cluster. Pretty much the only explanation for that is a bad cluster, unless perhaps it's reading some "intermediate amount" that happens to correspond with what's in the tank. Have you tracked the level as you drive to make sure the key-off reading is actually accurate and not a coincidence?