1999 5. Liter mercruiser with alpha one runs well but at about 3/4 throttle it’s rpms fluctuate between 4300 down to 3800 with a hesitation. WAs thinking of doing plugs,wires,cap rotor. Also need a new prop and will change that. Any suggestions would be appreciated. It has fresh gas and new gas filter already. Thanks. Rpms go down then back up and happen quite frequently