Large loss of power

Well the past 2 weeks in my 94 Z28,my power has been getting less and less, and my fuel milage has been going down as well. At the start i could do 60 in about 5.5 now its 7.4 and my gas milage has gone from 23 to 7, i replaced the plugs, wires, air* fuel filter, o2 and i hooked up a computer to the obd 1. there wasnt a code but i wanted to scan and see what all the sensors where running at, everyone of them read what the book said it should, i did a compression test and it passed pretty well, it seems to have little power under 3000 rpm's but then seem to pick up alot. and at about 50% throttle there dosent seems ot me much of a difference in acceleration from 50% and 100%. any idea's?

maybe your cats/cat??

Is it an automatic? I've got a 95 Z28, and it has been doing the same thing here lately. I did and changed all the basic stuff, too, and it didn't seem to help. On mine, I step on the gas and it kind of chugs a little, sounding like its just sucking down gas or something, and then at about half throttle it suddenly kicks in and picks up speed. I've also noticed a considerable increase in how often I'm at the gas station. And I used to be able to smoke the tires, but someone wanted me to here recently, and it barely even peeled out. It just seems like I don't have any power in 1st or 2nd gear or something. I was wondering if it maybe wasn't the transmission or something?

if it was the tranny im sure it would be showing up with a code

DOH!!!!!! i read the repair manual, i didnt realize that an "opti-spark" was the actual distribuator. I thought it was a distribuator-less ignition. When i did the tune up i didnt get a cap and rotor.... SO the loss of power, backfiring, slugishness, and the poor fuel mileage... im thinking is the cap and rotor... hehe... i guess you learn something every day