Has anyone hooked up an oil pressure gauge to actually check the oil pressure when the rpms are low?
This is first place to start.
The oil needs to be checked for evidence of sludging. If there is sludge in the oil passages it is harder for the oil to get to the top of the engine, as well as for the oil pump to work efficiently.
The 2.7L chrysler engine has several known problems resulting in low oil pressure and eventually locking up. The water pump was poorly designed which allows coolant to get into engine crankcase thus causing the oil sludge. The oil passages were designed too narrow, which combined with oil sludge causes engine seizure. And the PCV system is poorly designed. All these factors can lead to low oil pressure.
You need to have the oil pressure tested, and I would also have the oil checked for evidence of sludging. Even with oil changes every 3,000 miles, there is no preventing sludging on this engine. If engine has sludge build-up, you can try having it flushed out, but there are no guarantees.
If you would like to find out more about these issues, here is a good site to check:
Unfortunately, due to the severe problems the 2.7L engine has with oil related engine failure, I have to advise you on the worst case scenarios.