[kev2]

very likely a NP 241 ... before we sdjust inspect and generally tear into it...try shifing into R and then try to shift out of 4hi... sometimes they bind for lack of a better term, and the R kind of unloads them

This is a manual shift T case - direct linkage- if above fails take a look at linkage- a detent switch may be binding it..

As for milage - a 1989 360 - not a gas mizzer..... start with a code ck, then basics... vacuum, temperature, plugs, wires...

 

[ImperialCrown]

Really beat fluid can cause hard t/case shifting. Drain and refill should be about 2 quarts of ATF+4 (use the good stuff). Watch what comes out of the drain plug to gauge t/case internal health (this may not be the whole story, but an indicator). Linkage can also bind if it hasn't been used recently.
Different tire pressures and treadwear amounts can cause the forward drivetrain binding that traveling a few feet in reverse might unbind.
The growl is likely a failing bearing somewhere in the drivetrain or a sawtooth (cupped) tire. Maybe not the t/case. Try to locate the noise source first.
These were heavy, thirsty bricks.

 

[TWX]

Yeah. He's getting twelve mpg now, he'd like to get it up towards fifteen, but I think that's going to be quite the challenge given the weight and shape.

I've suggested that he change all fluids, axles, differential, transmission, etc, in addition to engine oil that he's already planning on.

It felt weak to me when I drove it, but admittedly I'm used to Magnum multiport 360s, not TBI, but I drive a one-ton maxivan at work with a whole lot of crap in it, so I did expect a little more performance for this truck than it delivered.