However BBforks, it is my experience that slipping clutches (due to an misadjusted inch spool or driver riding the inch pedal) will take at least about 45 minutes (and more likely an hour or 2) of -driving-, to heat up and transfer the heat to the engine cooling system so that it shows up in the engine temp gauge, however the torque converter stator being damaged will show (when using an infrared temp gun type thermometer) serious heat (230f) in the cooling line that comes from the transmission and that heat will be back to [almost] normal as the oil flows back to the transmission, within 15 or 20 minutes of driving (not idle sitting, but moving the truck).
I suggest using the temp gun, shooting the engine a few places (the 'freeze plugs' work best imho), shooting the radiator a few places and shooting the trans at the fittings for the cooling lines.