Ditto for me. 18 MPG last I checked with 285's. There should be a tag under the hood that tells you front and rear end types, gearing and other info.

 

bingo!!! thats what I had, but I just installed 235's(all six ) and 60mph is 2000 and 65 is right @ 2200 now. I have 4.10's and 5-speed. I was gonna change to 3.55, but after hauling the slide-in(2200lbs.)and the car trailer/'74 bronco(6100lbs)...I think i will keep the 4.10's...did great on the hills and @ 60mph, I get 15mpg! I dont mind taking my time getting there Chuck

 

i've got 235/85's right now and the rpms i listed before are what im running. I've lined up a dana 80 with 3.55's, so i'll probably buy that and install it and go without 4x4 until I get a dana 60 ring and pinion 3.55 installed.

 

I have the same truck with 4:10s, and 2000-2100 @ 65 mph is what I get.

 

I am running 285's and 3.55, but I think tranny has do a lot more that just gears. Same set up with my old stock tranny I was at 2100rpm, built tranny I can get as low as 1600rpm on a flat run and 22mpg

 

Shoot couldn't tell you from the top of my head on my gearing, but I have to go about 75-80mph before I hit 2000rpm, or be under a load. 65 mph @ 1550-1600 rpm.

 

4:10's don't necessarily get worse mileage than 3.54's.

 

4:10 and auto tranny everything bone stock (did have the IP rebuilt/recalibrated awhile back though) - not pulling anything I can average 21 mpg on the highway. RPMs @ 65mph about the same as yours.