6 BTA 330 ONLY MAKING 2650 HELP!

Quick question for you all:

Issue: Port Motor ( Yr 2000 Cummins 6BTA 330 1700 hours ) WOT only 2650rpm The starboard is at 2825rpm.

What I know:
Props are the same per scan, bottom clean, No load test engines do the same numbers in neutral, not noticeably more smoke in the air on port but the stern is a little more dirty at the end of the day on the port.

Both engines go up at the same rate. 1000-1200-1400-1800-2000-2200-2400-2600 then the port maxes out at 2650 and the starboard 2825.

I replaced the throttle cable on the port motor and still same issue.

Why isn’t the port making the last 150-175 rpms??

Thank you for your help this driving me crazy.

Respectfully,
Austin