So much uninformed speculation on this post it boggles my brain, fist right out of the gate, this was not the “ only” manual truck transmission installed in 80s GM trucks in fact it is kinda rare, the most common manual in 80s GM trucks was the muncie sm 465
with the granny low, 4 wd versions of the np440 were all cast iron cases , despite similar with the A833 used in the monster hemi motors of the mopar days the 80s version is rated below the 300 lb/ft range I didn’t see what rear gear ratio poster was running but with a 3.09/1 1st gear ratio getting to 15-20 mph before shifting has been my experience with this stick shifted slush box” slay slush box as this transmission indeed came from the factory with ATF as the fluid
