My starboard motor runs 250-300 rpm less then my port motor @ wot any suggestions? FYI 42 fountain w/700's and #6 drives.

Are you looking at the analog gauges or the smartcraft? If you have a bad ground they be way off on top. My Livorsi prop slip guage is digital and it is still off 200 or so RPM's up top compared to my smartcraft.

How many hrs are on the engines? Probably not enough to point to valve springs?

My analog tachs are off by 200-300 rpms compared to smartcraft. 6 drive boats are also very trim sensitive. The mechanical indicators may be not be exact. If you scroll through the pages on the Smartcraft, you will find a digital trim indicator on one of the pages. Compare that to the mechanical indicators to see if the drives are even when the indicators say they are. Mine are not. The numbers on the digital smartcraft for trim and the numbers for the mechanical indicator will not match up, but you can use them for an comparison. Good luck.