8 3/4 ring gear change for optimum low end performance
Guessing 3.91geared/5.2Magnum?
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I had a 92MPFI, like that; it was harder on gas too, the faster I drove it; even with the overdrive/LU
My tires were 235/75-15s about 28.9" tall, compared to your 28.0..
Mine was an extended cab/regular box, 4x4, Fuel mileage was Capital L, Lousy; so I didn't keep track much.
That 5.2M had a surprising amount of giddy-up for it's tonnage.