Wow had exact same experience with our 2017 Northwood Wolf Creek. The first several trips the pump (Shurflo 4008) worked fine then we had city hookup for a solid month. After filling water tank at campground next trip I could not get it going again at the campsite. Huh, we only used it about 2 weeks. Got it back home filled tank again, still no luck. I tried everything you did. Wouldn't even suck it up from a jug of freshwater. I would have even tried a shop vac if I'd had a clue. Pump screen was full of plastic debris but that wasn't it either.
Left camper at dealer for a month to get sliding window on front of camper replaced with a 1 piece unit, it leaked when traveling in the rain, so asked them to look into the pump too. When we picked it up the pump worked fine but paperwork said they couldn't reproduce the problem, Huh. No one could tell me anything but they did something I didn't to get it going.
Make sure you bypass hot water tank, which for me the end of the bypass lever will point straight up. I doubt you need a new pump, I could tell they didn't replace mine. Our pump ran fine but wouldn't pick up water as if it needed primed. But aren't they primeless? Has worked last few trips but I expect it to happen again so please post your resolve.