1990 c 1500 5.0 FI

i am wondering , what is the best way to improve performance in a stock 5 litre gm eng. without spending a lot or tearing into it to much ? i have installed flex fan ,in place of clutch type.am now wanting info ,replace the computer chip with a performer ,or direct fresh air to throttle body directly from the grill forced air ,or install a plate under throttle body ,has duel exauhst wit cherry bomb shortys 2 inch pipes from stock Y pipe. runs well for a 5.0 but could get better miliage and performance ,torque could use help low end ,and a small increase in HP wouldnt hurt ,moter has 28,000 on complete stock rebuild ,in 90 cheyenne 4x2 body wit 216,000 miles and no rust southern kentucky truck used by phone company ,has three spd ,no overdrive ,31/10.50/15 cooper tires , am getting about 9-10 miles a galon on reg 87 oct, about 12 mpg wit 97 oct, what can i do to spruce it up my old un rusty sleeper

Your getting some pretty poor mileage especialy considering there are so few miles on the engine, I regularly achieve 18 mph on my heavier larger truck with a 5.7 that has 200.000 k on it.
All the modifications you mentioned will help a little after each is installed and will compliment eachother.
But unfortunatly all in all there is no one item that will give you all the gains you seek.
The non OD trans your running is certainly a drawback in your wish for better mpg, and the engine your running has never been known for it's high performance qualities but since it's all stock you have no where but up to go.
The one good thing is with only 28k on the engine you have alot of time to play with it.

thank you for your reply , im ordering the chip for performance today ,and will install it , i also have a used scanner that i was told can set up this to match a 5.7 engine in hp and miliage we will see, it the scanner was used, but good shape, and will work on my 90 chevy. ill post when its in an let ya know .