Help with Trim, I think:(

[Eddie O'Neill]

Had my boat in the water for almost two weeks now. First of all, I am totally new to this so please bear with me as my explanation may not use the correct terms. I have. Four stroke 50hP yamaha on a 20ft boat.
Today I was out and operating the boat on full throttle, it reached about 5,500 rpm and was riding well. After about a half hour the engine revs dropped to 4,200 and I felt a fair bit of vibration from the rear. I stopped the boat, stuck it in neutral and check the revs on the engine, could get it up to 6000 rpm. Stuck it back in gear, but would only do 4,200 again.
I tried adjusting the tilt, but it made no difference.
Looking at the wake, there was much more turbulence from the prop than normal. I decided to head back to the dock and then I touched the trim button again and away it went back to 5,500. Tried to reproduce the problem but could not.
Any help appreciated. A total newbie here

[Bamaman]

I've had a stick get stuck on my lower unit a bunch of times, and it would to the same thing. I'd stop, kick it in reverse and back off the stick.

If it happens again, stop and back up. You never knows what comes out of the tunnel up front.

[Eddie O'Neill]

Thanks, that makes sense, if there was something stuck in there, would account for the vibration. I'll try the reverse trick.
Oh, and I am so glad a I bought a pontoon, best fun I've had in years, don't tell the wife:)

[HandymanHerb]

Weeds will do that in Florida, I use to have to stop on the other side of the weeds between lakes, reverse the prop to throw the weeds off and start again, same thing coming back

[Eddie O'Neill]

Yep, that makes sense to me. I'll definitely try the reverse trick if it happens again.

[badmoonrising]

Yep, same here when seaweed or floating sticks get stuck on the motor.