Generator failure: New Keystone Raptor

I have had a ongoing problem with my 2007 Raptor generator this past summer (5500 marquis gold) stumble rough idle then quit. Originally replaced the fuel filters and thought all was ok. Ran if a few times dry camping...only about an hour or two. I hardly ever use my generator, my genset had only about 30 hours on it total. Then over Thanksgiving I went to start it for my monthly start up and run time and had issues with it staying running again. Had 10 gallons of new premium gas in the tank and Stabil were added. The genset would only run when primed. Then would get a code 36. So I started searching and was figuring it was the fuel pump gone bad. Just yesterday i went out to troubleshoot. Before testing the genset, I took off my gas cap and ran the fuel station, pumped fuel from the tank back into the tank to keep the pumped lubed up. Then went and drained the carb fuel bowl to check for fuel...gas looked fine. So primed it up and hit the start button and the genset started and ran PERFECT. Ran it under load for 30 minutes. Not a hiccup. Thought WTF? So as i go around the fifth wheel i notice that i LEFT THE GAS CAP OFF. I was actually searching this forum to find out whether the gas cap for the Raptors was vented or non vented. I replaced my orig cap with a locking one 5 years ago. New cap time.