Honda spuddering, backfiring on highway, stalling at times, rough idoling and drive.?

OK I have a 92 Honda prelude with a h23 rebuilt engine swap. (so my check engine light never comes on). but i've been having problems lately with my car spuddering constantly. It does it alot while being on the highway but also backfires on highway when i let off the gas and then press the pedal is when it backfires. it only spudders when i give it gas. It also dies or feels as if its gonna die sometimes when driving through the city oand i come to a stop. i have some custom gauges one being a volatge reader and when on highway i can see it jumping from 12 to 14. but the spuddering is my main concern. I've replaced plugs (w/ the right gap), wires, cap/rotor (when i changed the rotor the problem got better but didnt fix it, it used to be so much worst), fuel filter, MAP sensor, and checked my vacuum lines. the problem is getting worst i can tell