If none of this works, you need to start checking other things like fuel pumps and electrical items. I just like to try the simplest things first and then work your way to the more technical stuff.
simplest thing would be a fuel filter.
I suspect its simply a matter of the slope on which you are parked. If it was leveled, I'd bet it would start and run.
2005 Newmar Kountry Star Gas 3742
Workhorse W24, 8.1L/Allison 5-spd
JT, Em & the boys, Kong and George (rescued grey tabbies)