My truck runs rough and loses power and the temp gauge shows false readings.

Sounds like you have a cooling system problem, possibly even a leaking head gasket, because if it was only a gauge issue, then when you lightened the load, the truck should still run the same and the gauge should read the same, not lower. I would use a scanner on the cooling system sensor, as you pull the plow, I'll bet that it goes up over 212, and when it does the head gasket starts to leak a little and then you get the misfires. I would have a shop do a block check on the cooling system, to see if exhaust gas is getting into the coolant, that would be a tell tale sign of a leaking head gasket. The fact that this happens under load is really a classic sign of a weak head gasket.