Got a great deal on a new 16x46 gt and put my 27 gdsd on it. Max speed is 20mph in deep water and 21 in mud. I thought it would push it a bit faster, but it did increase 3mph from the 17' Tracker I had. The current rig has gas tank and trolling battery up front and starting battery in the back. Ran 20 mph from 3300-3600rpms. If i trimmed up for more rams speed would fall off. Any ideas or similar rigs out there with performance like this?

Is that speeds solo or with someone?

Just me in the boat.

You should be faster. We have to eliminate a few things.
1. Is your prop warn?
2. How high is your cavitation plate above the water at max speed?

Prop measures 5.5" from center of shaft, so 11" total diameter. The plate was anywhere from about 2-3" out of water at lower rpm to maybe 6" on the higher rpm.

66 hours on the motor/prop. I have never really ran it rough or in a lot of mud or sand. Have hit a few stumps here and there, but the prop has no Knicks or bends in it.

I have never checked the belt tension. I will have to get a gauge. The motor seems to have plenty of power and torque and I was not expecting a speed demon, but I thought I could at least get about 25 mph out of it. The bow of the boat did seem to be running a bit high out of the water though. Next week I will try to get it out with another person to see if that makes a difference.

I got 24.5 out of my old 23hp. You should get 25. Check the bottom of the boat for hooks. That could also be your problem.