Full tune up will certainly improve gas mileage. plugs, wires, cap/rotor(if DIS, then doesn't have), fuel filter, air filter, pcv valve to name a few.
99 mpg
My 1998 S10 2.2L standard 5 spd averaged 28 mpg.
30 mpg hwy
Yes
No. Different generations of S10 altogether.
The 99 Chevy S10 does not have a fuel pump reset button. The pump is controlled by the relay unit.
See the related link for fueleconomy.gov.
about 27 highway mpg
I have a 98 S10 pickup with the 2.2L engine and standard transmission. I average 27 mpg.
With the 4.3 L engine and 3:73 gears, around 18 mpg.
I get 12 to 18 mpg with my 91 s10 4.3 4x4 5speed
My buddy has a '99 ZR2 with a 5 speed.