i need some advice so i can figure out why my gdlt 25 dropped rpms this morn. here's what happened.

i was running wot (just under 3300) trying to beat a storm in and the motor bogged down like i ran through some mud. i was in deep water, and the engine droppped to about 3100. it slowly dropped rpms while i was running in, and by the time i made it back to the ramp that was about a mile up the bayou the engine had dropped to just over 2500 rpms. once i got in the bayou, i pulled the prop out of the water and the engine ran fine at 3800.

the prop is in decent shape. got any ideas about why i dropped so many rpms within a short period of time? 3300 rpms to 2500 rpms wot in 2 miles of deep water, and 3800 rpms out of the water and i can't figure out why.

thanks,
mm

choke?