93 4x4 S10 Blazer lacking power and bad gas milage

I just recently aquired this blazer and have been having some slight problems. First of all, I'm only getting like 12-13 mpg from my vortec 4.3L. Also, it seems as if I may be lacking power. The truck will not even accelerate in overdrive, it has to drop down to third to speed up at all. It also just failed an emmisions test but passed when I poured some gauranteed to pass stuff in the gas. I dont know if this has anything to do with it. Any insight out there?

When driving at a constant speed does it like surge and have a hard time maintaining a smooth pattern? I have a 94 S-10 4.3 that barely passed emissions and it had horrible gas mileage and liked to surge. Short story--- found out that the electrical wires for my injector sys. was installed over one of the gas line tubes feeding an injector and wore a whole through(6 cyl. firing on only 5 not very efficient). Replaced spider injector sys. Now runs great.

No, it doesnt really surge. But I do have a hard time maintaining speed.

Does it start right away after sitting, say over night? Have you checked your vacuum lines? If nothing else follow them around and change them all out. The smallest hairline crack in a line will mess up your mpg and power.

Yeah, it starts right up no problem. I'll check out those vacuum lines though.

Good luck. One other thing if you haven't already done it is change your plugs, wires, cap and rotor(especially if you have no idea how old they are). On my 94 I take the tires off to get to the plugs through the wheel well---may take a little longer but at least it's a straight through shot at them and your not leaning over.