5.0L MPI low rpm at WOT

[Nede2]

I’ve got a 2006 Crownline classic with a 5.0 MPI and an alpha drive. Toward the end of last season we had figured out that the boat was running on 7 cylinders. One cylinder had no compression. We replaced one head and had a valve job done and put it back together. I had expected to be closer to the book WOT of 46-5000 rpm and about 45-50 rpm.
After taking it out this season it was doing around 41-42 down river at about 42-4300 rpm WOT. It currently has a 3 blade aluminum Mercruiser prop at 21 pitch. Im wondering where to start troubleshooting.

 

[Nede2]

I will add that the distributor cap and plugs are new. The wires are not.

 

[Nede2]

Took it out last night with the trim tabs taken off. They were on when I bought the boat. The black rubber type that are not adjustable from inside the boat.
After letting it warm up some I found that it was doing between 47-52 mph at a Wot of about 4900 rpm. Damn trim tabs…

 

[alldodge]

Thanks for the update, should help others