Tracker Grizzly 14/48 with Mercury 25HP Jet Drive Speed ???

[Weez556]

I'm starting here and asking for my Nephew. He just picked up a used Tracker Grizzly 14/48 with a Mercury 25 HP 4 stroke Jet drive. Said with 2 people in boat by phone GPS only 7 mph and boat will not get on plane just plowing water. Has manual jack plate lowered motor about 1 1/2" tried again same thing. Check other place online for motor height or setting and said seems close.
Any information or thoughts ? Or is that best it will do ? Thanks
Will ask in Mercury motor page also.

[High Tide]

I have a Grizzly 14/48 with a four stroke propeller Mercury 20hp. With two adults (400 pounds) and gear my top end is 22-23mph. I have trim tabs on the transom to produce a nice level ride.

Are you sure his engine is turning full rpm's?

Did he do a test run with the previous owner at the time of purchase? What were his speeds then?