I'm sorry maybe long but be patient.
I have an 89' f250 EFI 460 backed by a c-6.
Anyhow when empty with a 6-8% grade of roughly a half mile long, My truck will
heat up, the temp gauge shows around the r&m in normal and will ping like crazy as I try to accelerate up the hill, will have to feather off the throttle to get
it back under control and the temp slowly declines. So there's more, the other
day I had to refrigerators what maybe 500#'s anyhow another hill not as steep
as the first but nun the less it did the samething, heat up start to ping till backing off the throttle. So now I have 2000#'s of wood and im going over snogualmie pass in Washington roughly 30miles of hill from 2% to 6% grade at the last 3 miles, anyhow I kept my throttle steady at about 65mph and let the
truck slow down as the grade steepened and so forth, It would slow to about
50mph and hold steady without down shifting, and all along my temp would not
rise above the n in normal and would not ping not once.
So what do all ya think? my first thought is the TPS (throttle position sensor).

 

I think intake air temp sensor or MAP sensor. A mountain pass is both higher in altitude(lower pressure) and possibly has cooler air. That fact that it ran "well" in this condition tells me the computer is getting bad info and not correcting for lower altitudes and/or higher intake air temperatures.