engine stalls at high speed

[supcoinc]

I have a 95 Chaparral deck boat with a 4.3 mercruiser engine, the problem is when I go high speed the engine (after working for about 3-4 mins) stalls out. Gas tank has been cleaned, new carburator, new gas filter,plugs, distributor cap, water pump (told it might be an overheating problem) it will run fine if I just run at small wake speed about 5-10 mph. What is going on? was told ignition coil (do not understand that) oil sensor ground wire which goes to fuel pump was fixed (last time out wouldn't start until wire was fixed) running out of options without replaceing everything. Please help