Welcome to the prop forum.There is a Evinrude/Johnson Forum for service questions.
Sometimes we can help evaluate your performance here in props and help figure if its motor /boat issue or a prop issue.
The motor develops its hp at 5000 and the range would be 4500-5500.
Voltage at about 1500 rpm would be 13 to 14 volts.
Don't rev too high in neutral as it could trigger a runaway. 12.1V etc is standing voltage.