It seems to me that if the boat is slipping the first 10 yards (slippage = cavitation) you either have some crap in the pump ( im sure you already checked) or you have a impeller ware ring clearance issue. Your Ultra should be jumping out of the hole without any slippage at all.
BTW, If you decide to take your boat to a shop, make sure its NOT ADM boatworks in SoCal. You will end up spending about triple the price there and your boat will be in worse shape then before.
"Fellow ADM blacklister"