Low end performance/gas mileage

I've noticed for a while that my low end performance has been struggling (under 3000 rpm). When i first got it i could at least give it throttle from a stopped position and spin the tires a little on dry pavement but now it is very slow off the line. Also, my gas mileage has proportionally decreased. I used to be able to get a little over 300 miles to a tank but now i get between 250-270. Recently I have replaced my spark plugs, plug wires, air filter, fuel filter, oil and filter change, pcv valve and added a lot of fuel injector cleaner. this started about 4 months ago at the time that my transmission was slipping and I thought the new trans and torque convertor would solve this problem. I was wrong, any ideas would be appreciated.

I've noticed for a while that my low end performance has been struggling (under 3000 rpm). When i first got it i could at least give it throttle from a stopped position and spin the tires a little on dry pavement but now it is very slow off the line. Also, my gas mileage has proportionally decreased. I used to be able to get a little over 300 miles to a tank but now i get between 250-270. Recently I have replaced my spark plugs, plug wires, air filter, fuel filter, oil and filter change, pcv valve and added a lot of fuel injector cleaner. this started about 4 months ago at the time that my transmission was slipping and I thought the new trans and torque convertor would solve this problem. I was wrong, any ideas would be appreciated.

1995 = CPI Injector is probably leaking

Remove the top IMTV valve under the vortec name plate on the top of the engine and look down into it with a flashlight and look for golden washed spots and pools of gas.