So I have a few questions but first the info:

I use my 350 tpi firebird as a DD and i go through $60 a month or more in fuel.

improving fuel economy a tad:
I've already ordered an a/c delete pulley (pulling entire 80lbs worth of a/c parts out completely, aluminum driveshaft installed, conical k&n self built intake w/ descreened MAF. New hooker 2055 headers, 3" madrel exhaust and gutted cats to come this week. Seafoamed recently plenum, TB, Oil Crankcase, gastank. Switched to mobil1 synthetic.

What my engine is doing:
I bought a new head unit + 4 speakers, no amp for the car. Rarely use the speaker system, run a gps almost always powered via lighter-port. Rarely drive at night, NEVER use heat, A/C, etc, and most of my drive is 6 mile trips @ 45mph in fourth gear (Overdrive) around 2,000 rpm. Traffic is marginal.

Think i should add an under-drive pulley setup to further reduce load on my engine?

If so, Billet steel or Aluminum pulleys? My engine isn't pushed too hard usually, at most i pull out quick at a right turn or merge fast onto a highway once or twice a week. I asume aluminum would reduce inertia and slightly reduce weight but cannot handle as much punishment.

 

For what they cost I dont think it would help mpg

I run a high flow water pump to help compensate for reduced flow as at lower rpms and idle the motor will wanna heat up quicker. So far so good but honestly I wouldnt do it again.
Personally was after every bit of extra power and wanted something different but car would be just the same (I think) with reg pulleys.

 

i wish i only used 60 in gas a month lol... my truck uses a hundred every two weeks...(its also a lifted suburban with 35-12.50 tires) under drive pulleys probably wont show enough of a change to justify buying them. i was gonna put some on my camaro once im done with the motor, but i just dont think it will make enough of a difference to justify buyin em. i did all the ac delete in my camaro, removed the smog pump and the a.i.r. setup before i pulled the motor, and that made a difference.

 

No kidding. I pay forty a week to drive a few blocks to school and make roughly three 20-mile round trips to my parents' place, and that's not even in my Camaro...