Ok from a look at the post the only thing I see is well let me explain I have a sle version 95 bought from GM dealer in 99 passing 158 point inspection where I keep my car tuned to the fullest and the issue I had was plugs from experience with wires good and no other tuning issues check your oil condition if there a stong smell of gas or any smell of it at all there may be a minor misfie problem that isn't even visible unless u had this problem I had the issue with ngk plugs #1 the worst, then with all other types except rapid fire delco'* and split fires the real issue I found is that take the spark plug wires off the plugs and check the tips of the plugs for looseness if u find any loose change all plugs I had ngk and about 4 other kinds uncrew after use where the wire was securely fastened but with the looseness fuel was being passed even without smelling it out the tail pipe even ran good my empty pockets and too many trips to the pump had me investigate and solved it for me seemed like it wasn't possible to catch it driving, like it was missing 2 or 3 cyls sporatically . You can even have weak coils or even half of a coil out if all sensing components are good can't find the problem get down to the base of the engine and how it consumes fuel any thing else sounds like fuel injection then checking compression using bad oil too much tears internalls up.
PS Sorry for the text layout I type like I talk...

Actually..this issue ended up being a bad PCM. Wouldn't let the car go into open loop.

And to add what Boosty stated, when Mick and I drove to Enfield (appox. 500 miles) Mick and I were getting 24 mph......that'* 4.55 liters per gallon Canadian not 3.78 liter per gallon US. Once the pcm, iat sensor and the egr valve was change the return trip net us 34 mpg. All this thanks to jr's3800 and Boost Master Flex. Sorry Boosty.

I know..you are sorry my right foot won't allow 34mpg anymore. Glad that I was able to help getting the car back on its feet.

You guys ROCK!