I purchased a 2003 Holiday Rambler Vacationer with a W22 Workhorse chassis and Chevy 8.1 engine. I have always had Ford 460 or V10 engines, so I am not real familiar with this one, so I seek your adv...
Is the "check engine" light on or intermittent? If so, the first thing to do is check for any fault codes. If not, try the gennie in a can solutions and fresh fuel of the proper grade.
Is the engine running normally otherwise? IME, new tune up/maintenance parts rarely fix pinging issues.