Ok. So one thing I would offer is don’t involve more than one variable at a time. Pick a problem, and go through everything involved from beginning to end one step at a time in a logical order. Such as overheating- engine runs, you made the fan run and still overheating. What’s left? Water pump, possibly air pocket in the coolant, blown head gasket. I know it tries your patience but you can do it. Did you replace the fuel filter? This thing was on a construction site and you even commented on how dirty it was. What are the chances it could have dirt in the gas tank?
Good luck.
PS Don’t throw parts at it. That is expensive, time consuming and usually ineffective.
Pop Bob