With those symptoms, the only idea I can come up with is that your dipstick is off and your pan is overfilled. If your oil level is well over, you could then be hitting the oil with the crank and aerating it substantially. This would cause the pressure to drop off at higher revs or Gs, due to increased frothing, and possibly go back up a bit when you back off some. Then when you go back to idle, you start pumping unaerated oil and the pressure goes back to its maximum. As an aside, the 120 cold/60 hot idle pressures seem quite high.

If you haven't redone the pan or dipstick and used to not have this problem, then it's undoubtedly something else that I have no idea about.