I have a '88 Rinker 18' with 4.3 L Mercruiser and Alpha 1 drive...I currently have a dinged up 19" SS prop on it and it is over-reving. WOT RPM should be around 4200-4800, but at WOT it appears to be closer to 5250 now @ around 40 mph, I think speedo is messing up at times though. If just...