Another truck driver here.
 

I have an '88 chevy c1500 full size truck with a 350 v8 and an automatic transmission. I get around 17 interstate(70+mph) mpg now. I've always wanted to see the results of an aero shell because I knew it would improve airflow compared to anything else. I don't want to make my truck stand out too much though.

engine stuff I am interested in:
-electric water pump

-electric cooling fan

-removing air pump, I have a new 50 state catalytic converter that doesn't need an air pump.

I don't think gm made those full size trucks without power steering so there probably isn't a low geared steering box out there I can put on in place of the power steering. A larger steering wheel probably won't help enough to maneuver that big truck through parking lots.

If I could get the pulley system down to just the alternator and crankshaft pulley, maybe I could run without the alternator attached and charge the battery nightly.

EDIT: I remembered that I am not yet willing to give up my a/c, but I can get an appropriately sized belt to run only the a/c, tensioner, alternator, and p/s pump. So the only drag I would give up is the mechanical fan, mechanical water pump, and the air pump.

Aero/drag mods:
-removing windshield wipers.
-mirror delete or smaller mirrors, they're huge
-skinnier tires (when I need new ones) 255s on it now
-grille block except when towing
-Already have an air dam, about 8" clearance.

are all these mods effective? What fuel savings could I see with just engine, just aero, or all mods together.

I doubt you'll see much benefit from the wipers. Your truck is already an aerodynamic brick and IMO its not worth ditching them anyways.

The alternator delete is a good one. However, you'll need a deep cycle battery. The starting battery won't last long if you start to deep cycle it.

An aerocap would be your best gain coupled with adjusting the nut behind the wheel.

If you don't want to stand out, look into grille blocks, belly pans, and air dams. A site search using "aero topper" will bring up some good threads. I would not delete windshield wipers.

What is your RPM at 60 MPH?

about 1500, and there's almost no load on the engine, maybe some 2.73 gears could be put in place of the 3.08s that I have now?

If you are driving 70+ MPH, then engine accessory losses are small compared to aerodynamic drag. Your truck is already geared for mileage. If there's almost no load on the engine, a taller rear end ratio will help somewhat.

Go after the big aerodynamic losses - grille block, air dam, belly pan, and aero topper. I got more benefit from the grille block than my aero topper. That's also the easiest mod.