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
2018 Sunseeker 2430S with Trekker cap
and only rarely pushed by our 2017 GMC Terrain toad (4 wheels down)
Former Georgetown 330TS owner for 10 years with more mods than I can count.