You have a few options that are FAR cheaper than gear vendors. If you are up to it you can swap a 5.3 Chevy 4L80E combo that will double your MPG's. That swap can be had for around $3,500 if you find a wrecked truck, Youd just need a new radiator, custom mounts, and a T-case adapter or you can use the Chevy one. Or you can pick up a few MPG's by getting a 700R4 (not known to take much abuse) or the 4L80E with a standalone computer unit.
If your worried about expensive modifacations you chose the biggest wallet leech Jeep made. Sell it now if mileage is a concern.
I say this because the mods needed to yield better economy are not cheap. If you want more efficiency Id do the following. Upgrade ignition (check), install Edelbrock Performer with 4-BBL Carbof your choosing (They actually get better MPG if you keep out of the secondaries), Comp 260 cam kit it will remove the factory retarding and you'll actually unlock more power as well (you can use your stock valve springs or replace them), Doug Thornleys with 3" pipe, even using the stock manifolds and running a better flowing exhaust helps.
Lock out hubs are great, but the AMC 360 drinks gas regardless.
Your engine is an air pump. The more you do to help it breath, the more power it will produce with the same or less amount of fuel. Those mods will give you what will feel like a new motor. And they will help efficiency as well.
You can go a step further and just get a spare 360 and build it over time. Cores are anywhere between $100-$500 and all of those other mods won't cost near as much as the gear vendors. Then install a TBI from a Chevy and use the computer from the donor vehicle you snagged it from.
Its hard to push a brick down the road with a V8 and not expect it to drink like a freshman.
Wag Rebuilt 360, 260H, 727, Locked 44, AMC 20, 208, 31" M/T's, 4" Rustys, 2.5" Duals. SOON:SOA SF, 496, T400, Doubler, D60's, 37" M/T's <-TOY
Cherokee Rebuilt 360, 2" Duals, mostly stock. SOON: Hot Street 401, 4'' Rustys, 33" BFG A/T's maybe a T-case to get rid of Q-Track <-TOW RIG