I have a 23hp gdlt on a 15/42 Grizzly Tracker, currently getting about 19mph solo. Running with full gear and extra man, around 15-16. What are the easiest ways to modify this motor and increase performance all around?

What was your max rpm solo.
I can tell you a few simple things I did to my 23.
I have a 16x42 weldbuilt 23gdlt. Running 21-22 solo light.
20+ two people. I'm turning 3850-3900 solo. Don't want to turn much more on bronze bushings.
I have gained 3-4 mph with the following.
Drop in K&N air filter, pulled head and cleans up exhaust and intake ports with dremel.
Re-lapped valves and one of the more important steps...Adjust the govenor tab to 4000 out if water.
I'm not interested in putting after market parts on it.

I have a 23gdlt on 16/42 and it runs 23 with just me and gas. Only thing done to it is stock hutted muffler.

Gutted *

What Rpm you turning cody.?
Do you have a floor in your boat?

DD, If that tracker boat is the older welded modified V than that speed is good. IF it is the new 1542 riveted flat 200# boat you should be running 23 empty. With the throttle lever in closed position, bend governor tab toward front of boat till you are turning 3950- 4000 out of water.
Do not adust if you dont have a tach. Do not over adjust.

I don't know I don't have a tach . And I have a half floor of marine plywood that's it.