Motor City Mechanic has two Youtube video series regarding oil pump replacement on the 3.6:
Amateur advise again, but.......Before you replace the pump, drive the car with the display set to oil pressure. Oil pressure is typically around 40ish psi below 3500 rpm, and jumps to roughly 80ish psi above 3500. This engine uses oil pressure to control valve timing. If you are not seeing that, then either the electronically controlled valving in the oil pump is bad, or signal is not getting to the oil pump. Changing out the oil pump is not trivial, so you want to make sure you don't have an electronics problem before tearing into the engine.
Thanks for the link. I am told it is more complicated on the Grand Cherokee likely as a result of different suspension. The mechanic is telling me he needs to pull the engine to do this. Is that true. Is there a service manual that notes roughly how many hours this job is?