what gear should i put in a full size truck with a almost stock slant with a 18 spline long shaft 4 speed tranny...what rear end gear should i run?

What do you want to do with it?
Fuel mileage, high (low number) as you can get.
Performance, low (high number) as you can get.

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'81 D150 2WD shortbed 4spd OD.

What is the rear tire size (diameter) and what speed do you like to run on the open highway??
DD

Dusterboy,

Seems as if all of life is compromising.........I experimented til I got the compromise set that suits me well. Full size truck, 28 inch tires (275 60 15) 3.91 positraction pig, a "well built" engine that can breathe, (carbureted 4bbl), first ran a 833OD 4 speed, now a 727 automatic. Either one of these trannies suited me and I really like the 727 because I have a bad knee and in town driving was tough with the 4 speed. I don't drag race (don't know how) but will kick the random rice burner, BMW and Chevy from red lites for yuks if they invite the loss. Mostly road trips at 70 with homeowner around town trips tossed in for lumber, concrete, fence panels, and so on. Occasional Sunday drive for "engine conditioning" (75 to 95 mph)

rock
'64d100

My 79 D 100 was great with the A 833 OD P 235/75/15s and a swapped in 3.91 geared 8-3/4. Off the line power, in town acceleration and with the OD highway mileage. This was a stock 1 bbl motor, but I removed the converter from the exhaust.