I had an issue a few weeks ago where when I got to 3/4 throttle -
about 4000 rpm's - My oil alarm would go off (a beep every couple of
seconds) and my engine would throttle down to about 500 rpm's.

David... The following may be of interest to you.

(VRO Horn Warnings)

1 - A steady constant beep = Overheating - The V/6 engines, possibly some
others, have a fuel restriction warning which is also a steady constant beep.
2 - A beep every 20 seconds = oil level has dropped to 1/4 tank.
3 - A beep every other second = VRO failure, air leak in oil line, oil
restriction, (anything that would result in a lack of oil being supplied to the
engine).

Joe (30+ Years With OMC)