Gas Smell, Poor Mileage, and Poor Performance

    I have a 1997 Chevy S-10 with the 2.2L engine and 5 speed manual transmission.  For the past few weeks I have noticed a strong gas smell inside the cab of my truck.  I took the truck to AutoZone and had the codes pulled.  They are as follows: P0172: System Adaptive fuel too rich and P0300: Cylinder misfire detected (random).  Approximately 1 year ago, this same problem surfaced and I had the #4 fuel injector replaced because it was cracked.  After it was replaced, the truck still ran a little rough but the gas smell was gone.  I have checked and replaced all vacuum lines and replaced the spark plugs (~1 year ago) with Delco platinum plugs.  I'd really like to find a solution to this problem as my gas mileage has drastically declined (from ~27mpg to barely 20mpg) and the truck barely pulls a moderate hill in 5th gear.

Jonathan

Have you checked the fuel pressure regulator?
 
Also when you changed the spark plugs, did you change the wires and cap and rotor too?

Very possible you have a O2 sensor thats bad. Have you made sure your ignition coils are good?

When I changed the plugs, I also changed the wires but haven't, as of yet, changed the cap--after reading some old posts, that was going to be my next step.  I have also changed the manifold O2 sensor but not the cat. converter sensor.  I can see the poor performance and low gas mileage coming from these things, but what about the gas smell?  Is that old cracked injector coming back to haunt me?

Jonathan