I have low transmission lube pressure in my 846 Versatile with the 12 speed manual and am wondering what else there is I can check into short of tearing down for a rebuild.

Replaced lube pump, new filter, new oil (Mobilfluid 424), cleaned suction screen.  Oil cooler is clear...can see light through all of it.  Have 9 psi lube pressure at full throttle cold and 2-3 psi hot.  Warning light switches at 4 psi.  I unhooked it and cobbled up a gauge.  Inspected suction hoses and don't see any collapsing at full throttle.

What goes wrong in this transmission to drop lube pressure?  It's supposed to be simple and bulletproof.  Tractor has about 6000 hours on it. I've already done the pump.  What else is there I can check?

Thanks for any info.