I have no idea how what I'm going to suggest would work with any automatic, but there is a gear box called a "Brownlipe", and while the majority of them are for 1250 foot lbs of torque, making them large, and heavy, but they also made some suitable for a 1 ton. Most I've encountered were a 20 % under drive, direct, and an 15 or 18 % overdrive. Had one mounted behind the 5 speed and a 12 valve, was ideal. Since I didn't often tow heavy loads, once on the highway, could usually drop engine rpm by 450 when in the double overdrive of the 5 speed plus the browny. For that installation, I hung the browny from the cross member the drive shaft carrier bearing had been, making only one drive shaft require shortening. They are not real popular east of the Mississippi, but out west, I'll bet one can be found for $400 or less, in truck salvage yards. They are non synchronized, which requires a learning curve, and attaining some skill, but work extremely well, adding pulling power between formerly dead spots between large gear splits. If you found one, replace seals, have bearings checked, fresh lubricating fluid, and total including installation should be less than $1 K One caution, if you locate a 3 or 4 speed unit, make sure you get the shifter with it, as they use two push pull shifting rods, to get the miltiple speeds. Check it out, but I dropped enough rpms to raise my fuel mileage by almost 3 mpg average, plus in double overdrive, it would realy haul buggy, indicating well over the 100 mph mark.
