2001 Mercury Optimax serial# OT207468, engine runs fine 2000 rpm and above, but surges and hard starting. Replaced tracker valve, the air pressure at 80 psi but gage flutters fuel pressure at 90 psi gage flutters when engine running. Key on engine off, fuel pressure goes to 40 psi and within 2secs of fuel pump cutting off drops to 10 psi, pulled fuel rails back and no fuel injectors leaking. Any suggestions would be helpful.