There is one other good use for the SM420 1st gear on a "normal" truck (one that does not normally need to get a real heavy load rolling):

Win the "Slowest [non-stalling] Truck Race" at trucker shows/gatherings:
- set the idle as low as possible (no stalling is allowed)
- you can get out of your truck and walk along side of it, while you talk with onlookers
- they might have to end the race and declare you the winner, due to time constraints (if it is a 1/4 mile race course)

Two other good uses for an SM420:
- safely pull a VW beetle out of a ravine without burning a clutch (done that)
- drive up the side of a barn (almost tried that in an altered state-of-mind)?