Auxiliary transmission for heavy haul?

@JolliRoger Thanks for your input think we’re on the same page.
I’ve checked with several shops hoping to see the inside of a 4sp, no luck, I’ll be there if and when they tear into mine. Might be in a wheelchair by then, who knows.
You’re right about “a driver” “not a driver”.
In ‘75/‘76 I was the Kid and them old boys were just flat brutal if I broke anything but I learnt to take care of equipment.
I’ve seen 2 guys tear the crap out of their trucks, both tried to down shift auxiliary up hill loaded. Common sense and a little luck goes a long way.
When I bought truck I remember finding small brochure regarding the auxiliary that said to up shift trans to highest gear as speed allows. That’s sure contrary to what I’ve heard but That’s what I’ve done since day one empty and loaded, and now 575k miles later….
Bad part of this mystery is I’ll be retiring this November guess I’ll have to keep tabs on the ol’ girl to find out how long it lasts.