Agree you should fix the tach first. Also yes Mike at Skips will let you try different props till you get the right prop as long as they aren’t damaged. I always propped a boat to run right at the motor’s red line or max RPM level with only one person and a light load and trimmed out as much as possible without porposing on a smaller boat or slipping on a larger boat. Like someone said you can find a prop slip calculator on the interwebs. Good luck.
2005 Sea Hunt 212 Triton
“Head East”