What year/make/model of RV is it?
I'd strongly recommend removing the old gas- siphon, remove lines, etc.
The longer it runs with old gas, the worse it gets. If things aren't all messed up now, get the old out and the new gas in, maybe it will clean up.
Pull your air filter and clean it and the filter box and all the tubes from any mouse or squirrel nests (likely). You don't want to pull that into your intake.
Since you've run it a little, if you can get any plugs out easily, check each of them for oil, wet (not firing), burnt, etc.
The rest depends on the kind of RV itself.