My '98 Trooper with 88K miles has started to see a lot of fluctuation with the oil pressure. Most of the time it runs around 80psi and goes up and down 10 to 15 lbs with acceleration which is normal. Lately, on occasion the oil pressure drops by appx 30lbs. It runs at around 20 at idle and up to 50 at high rpms. Again, this only happens once in a while although it is happening more frequently. Any thoughts? Sticking pressure relief valve in oil pump maybe?

Thanks