The engine will definetely make more crankcase pressure at high rpm. I can't see how it's a blowby issue. No matter how much blowby you have, I can't see it blowing out the dipstick instead of coming through the breathers. No kinks in the hoses running to the flame arrestor, or anything like that? Besides, if it had that much blowby, you would DEFINETLY see the smoke. I'm betting on an oil cooling issue of some sort.

the hoses run dead straight to the Flame Arrestors ....and no PCV valve ..just a straight shot ..guess the hoses could be stopped up but I doubt it ....will check it .... I made some runs saturday late with the cooler bypassed ...even at 3-3600 rpm the oil pressure got less without the cooler ....it would run 40-45 and the other motor ran 60 ..which they both normally run until port motor gets low on oil ... I made a WOT run for a cpl of mins ....then came back in but didnt check anything .. it was late and was going to check today but with the weather and easter it didn't happen ...
Russ even stopped out in the lake and let it idle for about 5 mins and got back on the platform ..( you dont have one ) and looked for oil slick but nothing .... working 12 hour days this week ..6-6 mon-thur ..then off a week .. .. keep ya posted ....thanks

I wouldn't run it much more without the oil cooler. The oil will get hot real quick since it's running under a load all the time.
Your oil pressure showed that.

Yup ...I really didn't think I would see a big difference at 3K ...but it sure made a difference .... Still haven't climbed under the motor to see if any signs of oil but I doubt it ...
then just put it all back and go to the next thing ...

Aren't boats fun????

Another thought, you could have a leak in your oil pan.......

I had a similar deal happening to a 351 Ford motor, the problem was in the intake. The intake allowed exhaust gases to pass through to help warm up the inatke. Had a small crack in the exhaust passage. Everytime you ran the motor the oil stick would would push itself up.
Just a thought, as we had this motor rebuilt twice before we figured out the intake.
John