Multiple Misfire P0300

[PapaBear]

So.....truck got back on the road on Monday after Pacesetter LT's, catless Y, 3200 RPM Circle D stall, PCMforless wires, NGK TR6 plugs, heat socks, trans cooler added to truck. Also have IEATSRT8 intake, e-fans, 160 tstat, tuned by Alvin, Magnaflow 11229 no res.......

Anyway, today, got off work and headed to the Wadmalaw to put boat in water and go to restaraunt for some drinks. (Boat was at parents house so not hooked to truck cuz i know you will ask). Anyway, I had my friends new Gtech SS and wanted to see what it said would happen in the quarter.

So I got to straight stretch of road, stopped, hit record on Gtech, and flashed TC to 3000-ish and off I went. First gear, 5500-ish RPM and it started breaking up real bad, shifted, and I backed off. CEL was flashing and speedo said "0" which I figured threw the code. Pulled code on Aeroforce and was P0300, which I knew instantly was multiple misfire.

Didn't do any more runs so as not to hurt anything. Got to parents house and was talking to my pops (mechanic for 25+ years but no ECM experience) and he said he was willing to bet it was the plugs......and he wanted to see it happen. So off we went, turned out of dirt road, lined her up, and whaddaya know? P0300 at about 5500-6000 RPMs breaking up bad.

Any advice? Plugs were gapped to .035" as Alvin told me.

Could this be tune related, or something else? Truck runs absolutely perfect otherwise. Even WOT from a stoplight through 1-2 shift, no codes. Only threw the code when from dead stop, stabbing throttle to floor.