I run a 21 TRX with 250 Pro Xs My top end speed has decreased from 74 to 64 mph. The only change I made was I added an Ultrex. I am getting good rpm 5900 so not sure what is causing that much of a drop. Suggestions on what to check or tweak?

Mine was loosing top end and hole shot. Turned out the cup on the prop was gone or not where it should be. Hitting something or use in the water will wear it down. Prop work and boat is back good to go...

that's a huge loss of speed with just a troller change.
like dobbin said... take a look at the prop.

I agree it is a really big drop. I am going to run it this weekend with a Fury prop vs. the Tempest that i have on it now. I am not sure what to do after that. Maybe adjust the jackplate down?

10 mph is a bunch to lose.

Make sure the hull isn't full of water.

Make sure the boat's load is balanced as best as possible.

Have a Mercury authorized mechanic test and evaluate engine performance.

Send that prop to Josh at Steve's Custom Props and have it tuned up.

I've been told 1 mph per 10 lbs on the nose. I guess if you added 100 lbs it would be about right.

if the bow isn't lifting as much as before the troller change, then yes. drop the jackplate
down 1/2" and see if that helps.

I�d pull the one bolt holding the Ultrex to the mount and leave it in the truck for a few minutes. That would let ya know if the ultrex is the culprit.

Thanks for the ideas. Going to start with different prop first. Plug is removed, so I don't know if a Triton hull can trap water. I guess I can take the Ultrex off to see if that is what is causing the issue. From there I guess lowering the jack plate would be next step. I will keep you all posted. The weight difference in a Fortrex to Ultrex is supposed to be 13 pounds

If it started after the trollers take it off and try that first. That is the simple test.

i can't see 13 lbs making that much of a difference.... but, ya never know. these boats do some silly things
i had an ultrex on my last stroker.. it was still super fast.

weight on the nose is multiplied at the transom. do one thing at a time to try to determine the problem

may lost fire on 1 cyl.

Its NOT the TM change. Either the prop or the motor.