Lots of variables. Hours on engines? Compression and leak down test? Pulled valve covers looking for broken springs? When were top ends done? What props does your test report say the boat should have, brand and 4 or 5 blade? Props spinning in? Props in very good condition, have they been measured and checked for true? Thats just a start for ideas.

You may also want to post this question in the Fountain owners forum. Lots of knowledgeable people there.

My report has 84 on it, I normally can hit 85, lots of time 82-83 no problem full fuel load easy.

My buddy just got a 35 EX with 525's and report has it at 88, there is issues with props on his but so far we have seen 87 with him, me, and our wives, lots of fuel, junk they take and Florida heat (two weeks ago).

Those reports are really pretty nice, they show how the boat was ran and set up to hit the posted speed. I don't remember seeing other manufactures doing that but maybe they did.
All that said you defiantly need to start looking at things.
Your numbers show prop slip 25% - 28%. Something not right.

The 35 I said of my friends boat someone had cut the diameter down on them. Don't know why, but take one step at a time till you find it.

Is it a 38 you have also?

The semi-staggered 38 should run over 90 with ease. You have either some very tired mills or some hook in your hull - or both.