I have a 28 foot walk-around with dual chevy 350 inboards, velvet 71-c
transmissions and 16x18 props. Loaded weight is probably about 12,000.

The port engine will rev all the way up to 4200/4400 rpm at WOT and will
cruise in the 3200-3600 range. The starboard engine maxes out at 2800
rpm and won't go beyond that under load.

Both engines rev-up equally in neutral and compression tests were fine.
Had the boat hauled and the bottom and running gear are clean.

Any thoughts as to where to look for the problem?