In 14 years I've not had a roughness problem. I suspect one or more cylinders are not properly firing. It could be ignition, fouled plugs or defective coils (these engines are coil on plug). It could be clogged fuel injectors; while these engines are manifold injection, there is an injector for each intake port. The engine control computer probably knows what is happening, so it would be useful to read the onboard diagnostics codes. Rough running is not usually a transmission problem.
Another source of vibration, but not roughness, would be the driveline, most often an out of balance driveshaft or worn U-joints. RV chassis get extended, extended driveshafts have to be fabricated, not always well balanced. But vibration, not running roughness.