When driving at 55mph at 2800 rpm during acceleration to 3800 rpm the oil pressure drops from 50 psi to 20 psi.  What is happening? I get worried and shut it down.

everything new, only 3000 miles, makes about 400-425 hp, runs strong  

Are you running a stock pan?  If you are I would get a 7 quart after market one.  If you have a 7 quart pan was the oil pickup installed properly?  With a high volume oil pump most of the oil could be in the upper part of the motor.  Or the pan may need baffles to keep the oil pickup in the oil.  You could add a half quart over full and try it.  But don't run it very long.  If the crank is in the oil it could foam.