Originally Posted by dawktah
All info says go to a 19 or 21 degree prop, since that will lower my rpm at WOT.
Don't go fitting tabs or foils until you've got a reasonably running boat.
Do the checks on the engine trim as suggested. Be aware that most outboard motors have a pin through the lower part of the mounting bracket which limits the amount of 'in' trim which can be applied. If this pin is too far outward, even full 'in' trim can still be too far 'out'. I hope I've explained that ok. The pin can be moved to an alternative set of holes to make adjustment. The engine can satisfactorily be mounted with the plate below the bottom of the V if necessary, although folk tend to go for high positions generally, 25mm below the V is still a good position in order to bury the prop more.
However, if all engine rigging is fine and you are happy with your boat driving ability, the characteristics you are describing would lead me to reduce the propeller pitch. What you are experiencing sounds like the prop breaking away because it is too highly loaded and this causes ventilation (not cavitation). When/if the boat gets over the hump and planing, the load on the blades is lowered and it may regain its grip on the water. It may also account for you feeling the boat is very quick for 3800rpm. It could be you're closer to WOT than you realise.
The cavitation plate is properly known as an anti-ventilation plate. Cavitation is an entirely separate phenomenon.
To sum up, make sure the 'in' trim is correct, engine height is correct and then, if necessary, try a lower pitch prop.