Rpm gauge

I’ve got a 2006 202 Blazer with a Yamaha 250hp VMax HPDI that’s been rebuilt and I was told has a kit on it to make it a 300hp it’s got a Yamaha Vmax series 27p prop and a lower water pick up nose cone. My prop to pad height is 1 5/8 below pad but when I trim up the boat gets uncontrollable when I get about half my boat trimmed out of the water. I done some reading and one post said my motor may be set to deep so I raised it up to 1” below pad. Took the boat out and it jumped out of the hole great and seemed to be running and handling great! I glanced down at my rpm gauge and it goes up to 7000 and was setting about where 9000 would be if it went up to 9000. So I eased the boat back to land and came home and dropped my motor back down to where it was originally. The highest rpms ive ever seen with it at 1 5/8” below pad was about 6200. So after putting it back to that I went back to the lake and I’m cruising along about 45mph and look down and the rpm gauge is setting at 8000. I know that can’t be right because it’s never got over 6200 wide open at that height. I’m idling at about 1200 rpm according to the gauge which sounds high to me as well. How do I check my gauge? I recently had a whole new/used midsection put on my motor is there something that could have gotten hooked back up wrong or something. My prop also has a huge gash in it but that shouldn’t make my rpms that high I wouldn’t think. Any advise is appreciated. I haven’t had this boat very long and the one I had before it was just an older stump jumper so I’m new to the tuning in process of a nice fast boat.