I'd start with removing the rad and cleaning the cooling stack (A/C condenser, intercooler, trans cooler, and engine radiator). If it still overheats, there might be an issue with it.
A couple of questions:
- Is the engine stock or does it have a tuner/box/chip/programmer on it?
- Is the factory exhaust still in place?
- Do you have any type of bug screen or stainless steel grill inserts in place?
That's a big RV with about an 18,000# GVWR, 41' long.
2013 Fuzion 399:
Shipping Weight - 14100
Carrying Capacity - 3900
Hitch - 3500
Length - 41' 0"