suzuki dt50 slips even though new prop installed!

[prewired]

okay, so the problem happened before xmas & hasn't been delt with until recent

anytime the boat is under throttle i manage to obtain just under half throttle

the motor then revs & stops powering along ( feels as if prop stops spinning )

we've since purchased a brand new prop for $200

did NOT fix the situation what so ever

we performed an oil change and flush this morning for the bottom leg.

did not show any signs of fixing the issue either.. ( old oil smelt burnt and was black in color )

what could possibly be the issue?

has anyone ever experienced this issue before?

[seaox230c]

Run it for a while see if the new oil turns discolored...if so you have issues inside the lower unit. To absolutely ensure the prop itself is not slipping...do you have a removable hub like a merc flo torque or a rubber press in hub . If rubber make a paint line on the metal lip of the prop and one on the rubber hub and test the prop. If the lines move apart then the prop is slipping...but if your oil continues to darken then you have some issue inside. If the gears are slipping you should feel some sort of vibration or noise