Misfire P0310 P0301 P0300 on Stock ish 2001 GTS

[MH60M]

SOLVED! Do a Smoke Test! This issue was caused by Bad Intake manifold gaskets in a hidden area.

UPDATED: 8-12-19

So, I’m at a loss......P0310, P0301, and P0300 misfire codes at cruising speeds. It doesn’t do it at idle. Car is a 2001 GTS w/headers, HF cats, catback. I’ve been troubleshooting this for years and not driving it much because of it.
I’ve replaced these parts one at a time to try and isolate the issue. I’ve also checked other items.

Replaced:
Spark Plugs w/gen3 Champions
Wires with “Quality Wires”
Coils With Demon Coils
Fuel Injectors w/good used set
Fuel Filter
Cam Sensor
2001 PCM
MAP Sensor
o2 Sensors to NTK...OEM
Replaced Vac Line from Air Filter box to Intake/Valve Covers



Checked:
Fuel pressure at idle
Fuel pressure at cruise and WOT
Compression of all Cyl
Leak-down of #1
Valve springs-Visual
Vac System-Visual
Evap System-Visual
Battery Voltage
Grounds-Visual
Removed Battery to Ground Wire, Cleaned and Re-Installed
Ground/Reset PCM and reset adaptives via Doug Levin procedure