CM871 oil pressure

[Bigstank]

Hey guys need some help here. Got a 871 in here that's been de-mandated by @Mr.Hagg. problem I'm having is oil pressure usually runs 35 but lately it's dropping down to 25psi at 1300-1400 rpms. Idle is at 20 but if I idle up to 900rpm it goes up to 30-35psi like it should. But if I kick it up to 1400 it drops to 25psi when at normal temps. Now when I let it sit for 30 minutes off then start it she's normal again 35psi and 20 at idle. Is this a bad oil sensor or do i need to get it to Mr.Hagg for inframe time. Shes only got 762,000 on here and she runs great with high fuel mileage up in the 6.5-7's. She only uses a gallon of oil between services @ 15K..... thanks