hpdi 150 stalls at idle and won't run over 3500 rpm

[bdhall54]

I have a 2004 Z150TXR the motor has never given me any problems until now. It has 1950 hours and has been maintained regularly. This past weekend it was running fine. I was running at 4500 rpm and throttled back to make a turn. When I powered back up I could only get to 3500 rpm. No indicator or alarms. Oil level in bulk tank is good, oil in onboard engine is good, oil pump is working when
i used switch to fill engine tank. Since this issue, I have replaced fuel/water seperator filter, VST screen (VST was spotless), fuel filter in water seperator on engine, All filters were very clean. I also replaced spark plugs. No change. The motor will not idle and runs very rough when it does start. I can run it in neutral at higher rpm's. I am at witts end. Should I buy the YDS software? I am somewhat savvy about computers and have good mechanical skills, but I understand these engines have many safety features on them. PLEASE HELP!! Also, my batteries read low but motor starts and shows charging at 13.7V

[99yam40]

what do you mean your batteries read low?
low voltage can affect some motors.

I think YDS would be a good tool to see what is going on.
fuel pressures, switches made or not, injectors operating and lots of stuff.

but then you would need to know what is normal also

[bdhall54]

voltage on guage reads 12.3v before starting. I have purchased the YDS software and expect delivery by mid week. Hope this helps!
Where can I find the COM port on the engine?

[TownsendsFJR1300]

voltage on guage reads 12.3v before starting. I have purchased the YDS software and expect delivery by mid week. Hope this helps!
Where can I find the COM port on the engine?

My F150 is on the front (facing forward), more on the port side (yours may be different) with a gray cap on it. Attached to the gray cap is what appears to be fishing line (prevent loosing it).