The 58mph@4600 rpm is correct with a power tech 20 pitch

check your timing. mebbe you don't wanna adjust cuz computer will just compensate, but see what idle is and see what 3500 with the advance all way in is timed at. sounds like it is too retarded. the timing, i mean...you might want to take off sun pad-hatch and have a buddy run it up on plane while watching timing advance. the computer might advance differently with no load on engine at higher rpms on the hose in the driveway.

Idles perfect at 600-650 rpm. How can I check timing without the scan tool to set in service mode?

I'm sorry Martin, most of my posts were based on me thinking you had a 7.4l mpi, which is the 330 hp cast internal engine. You can build up what you have fair easy, my bad :/

So if you are going 58 mph with a 20 pitch at 4600 your slip would be ZERO (impossible) or you have a 1.36 ratio drive (or even taller). You might have other problems but the DRIVE RATIO is your main problem. You need like a 18 or 16 pitch prop to get your speed and rpm's right but that doesn't really exist in a stainless bravo prop so what you really need is to change outdrive gearing to 1.50. Your only running 4600 with a 20 pitch, your motor peaks at 5100-5200 so you are probably about 40 hp or so BELOW the peak , until you resolve this you will chase your tail, Smitty
I would buy the right drive gears or a diffrent drive.

He's turning 4600 with a 20 pitch though, if you crunch the numbers he must have a 1.36 ratio drive and boat is still propped too tall, needs correct gears before he changes alot!\
http://www.rbbi.com/folders/prop/propcalc.htm

Then something is not right. It should run at least 60mph at 4800rpms+.

Why not just buy a 40k boat that is worth 40k instead of spending 15k on 25k boat that will still be worth 25k when you're done.

Griff, if you crunch his numbers (58 mph with 20 pitch at 4600) it comes up as ZERO slip with 1.50 gears, boat wont pull a 23 except to 4200, only turns a 20 to 4600 BUT most the speed is there), I strongly feel he has a set of 1.36 or taller gears in hbis drive, he will NEVER get it to run right until that is taken care of, Smitty

agreed....my 270 laser ran 61-62 with the 454/385 , bravo 1.5 and a 21P mirage...4900/4950....before i added the whippled engine !

Yea it's a 454 mag MPI 385 hp