Rpm's at speed are dictated by the final gear ratio. Being this is a low geared 4X4 and a manual 4,000 rpm at 75 sounds about right. That truck would have come with either a 4.10:1 or a 4.56:1 rear differential depending on tire size. P22575R15 tires were 4.10, The optional 31" tires have the 4.56 gears.
If you run the numbers the 4:56 gears run with the smaller 28" tires shows right at 73 mph at 4,000 rpm.
I would say to check which gear ratio and tire size your truck came with first. If it has any type of towing or off road package it may have the 4:58 gears.
Friday, February 2nd, 2018 AT 10:24 PM