4x4 LUV pickups only came with 4.10 gears, for it to have 4.56s (& the 4x4 to have worked without binding) both the front & rear differentials from a '84-'87 Trooper would have had of been swapped in. This is a very involved swap, so I can pretty much guarantee you have 4.10 gears. If you are able to count the front diffy pinion gear teeth 4.10s=10, 4.56=9, both ring gears have 41 teeth. I suspect you are using a too large tire diameter when you plug the data into your caculator. Go measure from the ground to the wheel center of one of your loaded tires inflated to the correct pressure. This is the rolling radius, twice that is the tire diameter you should be plugging in. This will be smaller than the advertised size, & remember that the tire diameter decreases as the tread wears. The advertised tire size is very seldom the actual tire size, it just means the tire is bigger than the next lower series & smaller than the next higher series. I have two trucks, each with a different brand of 31-10.50R15 tires. Each brand tire is actually more like 30.5" in diameter when unloaded. The loaded rolling radius is about 14.75" on the lighter truck, even less on the heavier. If I plug in a 31" tire diameter into your calculator I get a significantly different speed for a given rpm than what I am actually travelling.
_________________ '78 Chevy LUV,1.9,4sp,headers,31's,SAS Dana 30,Dana 20,SOA rear w/Aussie Locker, rough body, bought new 12/4/78. '87 Trooper,2.3,5sp,headers,31's,ball joint flip & spacer,Aussie Locker rear,Superwinch hubs,brush guard w/5.5K winch,more to come.
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