From what I'm reading, it sounds like this problem is clearly with the performance of the Ford engine, and nothing from Forest River.
Your original posting mentioned you had been to a dealership, but I'm not sure what type.
My suggestion would be that you take it to an authorized Ford dealership. The engine compartment and working of the motor are not foreign to them and they would be the people to see for getting your trouble resolved.
Ken and Terry
2010 Georgetown 330TS being pushed by our
2017 GMC Terrain toad (4 wheels down)