I's still say it's the prop although the fuel pressure does sound light....I had the same problem in my boat after building a hot 350. As soon as I got a properly pitched prop it really woke up. I'd say 21 degrees minimum with that motor. Thats what I'm running on a 21 ft stingray with a 350 horse 350. It will get up to top RPM slower but won't cause the cavatation (Air space behind the prop) that a lesser pitch causes with a high HP motor. I tried the stock 19, a 21 and 23. Off course then I smoked the outdrive. Hey guys look it's some kinda silver gear oil in there. No man that's gear soup. What kind of hull are you running?