5500 Onan quits after 1-2 hrs use, then starts back up

Onan 5500 Marquis? They don't have inverters as far as I know. Check oil level and suspect fuel pump. With genny not running, press stop switch (prime) and listen for the fuel pump to run. When genny quits, immediately try that again and listen for fuel pump. Fairly common failure mode for fuel pump. They overheat and stop running, cool down then start running again. With sufficient load, sounds just like you shut it off, no surging.