SupermanZ28

I've got a 95 z28 and I'm having some problems with my build. I've got a 383 stroker; did a mail order tune from Harris Performance. It's been acting funny for a while, but I just assumed that it was bc I needed to get it dynoed tuned. I do have tuner cat, but I haven't used it yet. Before it messed up, car ran and idled fine, just ran a little rich.
So for my problem... Used to do highway pulls and stuff (esp when running late to work) Put the car in 4th and open it up... Hit about 120 and shift into 6th to cruise, right when I shift, car cuts off. I either have to drop it into 5th or back to 4th to jump it back off, it jerks and then cuts back on. Did this for like a week or two up until about a week and a half ago. Left a traffic light and shifted into 2nd at about 3k rpms, pressed on the gas and car started backfiring, got scared and shifted into 3rd. Backfiring stopped until I pressed on the gas again and it backfiring, immediately shifted into 4th, and it stopped again. Cruised in 4th at like 25mph until it started slowing down, shifted back down into 2nd and it starting backfiring again, so I pulled over and cut the car off. Did a visual check and nothing looked wrong, went to start it and nothing happened. I thought it was my fuel pump bc my injectors were basically maxing it out the stock one, so I installed a granatelli 255.
Tried to crank it up and it won't fire. I know I have fuel pumping from the pump, I've got spark, I've got compression, and I've got air. Motor will crank, but won't fire up. If you turn the key back and keep your foot on the clutch, you can hear the motor slow down and intake backfire (very quiet boom, boom). I have no idea what is going on, my only thought now would be my pcm. Please help, want my baby back on the road.