1983 Ford F-100 OVERDRIVE

Look on the drivers door post, find the label, in the box marked TR, does the letter T appear? If not it's not an AOD tranny.

yes there is a 'T'.
It shifts at 45, I am assuming that is the final gear. It is clunky sometimes but shifts. I wonder if the mpg is normal at 13? I lowered the tail gate and it got 13.5 mpg.

Only thing to check is tune up specs, and possible band adjustment, it's a fairly cheap adjustment, any tranny shop can do. I don't know if 13.5 MPG is normal, I dont think older trucks did much better than that. Clunks can also be caused by worn u joints, and tailshaft bushings, and pinion bearings at the rear end.

it is your rear end I have same truck with 3 on the tree 3.8 six and I get 27 in town 32 on hwy me gears are 2:73 look at door sticker and look up code

it is your rear end I have same truck with 3 on the tree 3.8 six and I get 27 in town 32 on hwy my gears are 2:73 look at door sticker and look up code

Was this issue ever resolved. jongustafson, did you check the tuneup as directed by our expert? If not, you should. Fordsixguy also presents a good answer. If the gearing in the differential is too low, you'll have to wind the engine higher than it should need to and you'll get worse mileage.