280 Misfire and water pressure issues

[Great East Predictor]

Have an 01 280 that is acting up a bit. To start it shows about 13psi of water pressure on a DDT before the motor is even fired. Once running it stays about the same but one you get on it psi rises on computer, and can get to 30psi while at speed. Occasionally misfires on #1 and #5 when cruising, and get's much worse as rpm's rise, has a hard time getting over 6k. Compression good, leak down good, new plugs, swapped coils, fuel pressure checks out fine, put in new water pressure sensor and same result, even swapped out engine wiring harness thinking there may be a short, water pressure is right where it should be on a mechanical gauge. Anyone ever had anything like this?

[Dave Strong]

If you have tried a known good sensor and harness one would think ECU has issues. Clean and check all grounds.

Dave

[Onetime]

Look for a lose or not connected ground.

[Great East Predictor]

Thanks, yes I used a known good sensor off my 225x and a brand new one, both with same results.
I'll go through grounds again but touched about all of them changing engine harness.
Think my next move after tinkering will be to get ECU tested. Any recommendations? Thinking either brucato or Simon.