Had smoke test (zero leaks), leak down test (0% leakage), compression test (great across all cylinders), boroscoped cylinders (they look good and tech said piston heads look clean and new). Changed injectors, plugs (2 step colder, NGK/Brisk), gapped down plugs between .020-.024, new oem coil packs, coil ground kit, newer version oem pcv (BL), unitronic catback exhaust, new vband clamp, walnut blasted intake valves. Vortex XL, precisionworks mpi w/ 1300cc injectors, rs3 brushless LPFP, stock fuel lines with check valve removed, AMS Carbon Intake, DBV2 Turbo inlet, first revision map e85 EQT custom tune. Still getting EPC though less frequently after recently installing new unitronic cutback exhaust, when above 5500-6000 rpm and 90% throttle to WOT. The scanner shows codes for cylinder 4 misfire and hide cylinder. Sometimes showing multi cylinder on both 2 and 4. 90% of time this happens I see just cylinder 4 and other 10% both cylinders 2 and 4 misfires. Restart resets the hide cylinder and EPC light and the car drives normally afterwards. All this EPC issues noticed after starting to take logs for EQT custom tuning. Also all changes and diagnoses was done after having a money shift event like 4 months back during 93 tune logging. So though tech diagnosed the car, they really do not think it is internal issue, but more exhaust or tune related. Do I need to rebuild the engine? Anyone else have any ideas what I can try/test to know if I need to rebuild engine without throwing parts at the problem blindly? Car drives normally except for EPC when driving aggressive and near WOT above 5500 rpm? Car only has 44K on it. Help! Any ideas? AP3-VLK-003 v1.7.4.2-23430 Vehicle Name: USDM Volkswagen CCF Mk7 Golf R / Audi S3 (CYFB 8V09C0BB01) Vehicle ID: VLK_CYFB_8V09C0BB01 (Installed) Serial: VLK0303046 Upgrade Serial: 00000 Original Serial: 63a00be6 ECU Reflash map: EQT - Vortex XL E85 1.01