My Nitro overheats when it sits at idle, and it is only 32 degrees outside.

Water pump is good, thermostat seems to be working properly due to hoses aren't hot, and its not steaming when it does it. Just the temp gauge registers hot. then once driving (moving) everything is fine again

Yep that sounds about right, except for the hoses not hot...should be same as engine temperature....... Threes must be a problem so.. same answer!!

Thanks! I will change the relay for the cooling fan and see if that fixes it.

No, let the engine run at idle until the fan comes on or it gets hot... CHECK fan operation..don't start putting parts on it!