oil pressure issue JD 650J

question for any of you out there with more mechanical know how than I. I operate a 2007 JD 650J LGP (see avatar) configured as a Fire Dozer (Tractor-Plow). Engine currently has 1939 hours on it. On the last couple of large fires I was working, starting having an oil pressure issue. OP normal runs on the high side of the dial (upper 2/3rds). On several occasions, and only after about an hour of "on the ground" time, plowing and then blading out fire lines, oil pressure drops to below...

oil pressure issue JD 650J

oil pressure issue JD 650J