performance of car continuing to fade away

[richie]

The mileage is 137,000 and the mods are 3.73's,flowmaster exhaust,asp pullies,march ram ram, koni yellow struts,,130amp,alternator.The rest of the car is stock.I had the injectors cleaned with the type that the car runs off of and tthat did nothing.The car used to vary every once in a while on how much power is had but now it just doesn't accelerate like it used to.I just bought a noid night to test current to the injectors but can't get the harnesses off.I also bought some longer tubing for my vacuum gauge so I can run it into the car to test vacuum while driving.How can I test the injectors to know if there flowing properly?The cats have never been replaced or messed with at all.The car is a 89gt 5sp.