Oil pressure goes up and down
Possible your pump is starting to go, or some debris in the engine. I'm not a fan of power flushing a car but I think you should have it done, its cheaper then replacing the oil pump.
it could also be a sending unit how is the oil level . how many miles do you have on it and is it new oil? dose the motor rattle or make noise when it goes down
CHECK WIRING ON THE UNIT
Looking for a Used Grand Cherokee in your area?
CarGurus has 73,673 nationwide Grand Cherokee listings starting at $1,500.
Search Jeep Grand Cherokee Questions
Jeep Grand Cherokee Experts