2000 Lincoln Navigator Stalling at low RPMS sporadically

You will need codes any auto zone will give them to you free. Once you have codes you will have an Idea what to repair.

Check IAC sensor,for low idle.

Your friend could be right. Normally if you have a cylinder miss or a problem with the transmission you would get a check engine light and a trouble code. Low fuel pressure may not show up like that.
You may want to check fuel pressure at idle and on the road.

Is it a clicking, Clacking, or clunking noise.?

The most common problem with stalling due to low rpms is the idle air control valve. this valve is what controls the idle and keeps the engine at the correct idle this is the first thing i would check and also make sure the throtlebody is clean, most of these type of problems are due to that valve good luck.

I don't know how much oil you had to put in but it sounds like you have maybe more than opne issue and both sound major. One is engine reving and speed not picking up sounds like trans problem. Two the engine shaking and making noise and being run low on oil leans toward possible engine damage. If your mechanicly inclined check all fluids and when checking trans fluid smell it. If it smells burnt the trans has been damaged. Check oil pressure and make sure coolant is full.You may have to take it into the shop.

The idle air control (IAC) valve assembly on a combustible engine monitors and manipulates the amount of controlled air moving around the throttle plate. The IAC valve is managed by the electronic control module (ECM) of the engine, which calculates the position of the IAC valve. Voltage pulses called counts extend and retract an internal conical-tipped shaft called a pintle inside the IAC valve. When the pintle is extended, the cone-shaped tip positions itself closer to the air inlet and restricts the amount of air allowed to pass through the throttle, building up more air around the throttle plate to increase the rpms of the engine. When the pintle is retracted, it moves away from the inlet and allows more air into the throttle away from the throttle plate, decreasing the rpms. The IAC valve operates and adjusts constantly while the engine is running to help prevent the engine from stalling or surging. This will not cause the engine to misfire!! Hopefully this helps

your idle speed too low.take it to a dealer.they have to reset idle.it should be 600-800 rpms.when you turn on air conditioner.the computer steps up idling to keep engine from stalling .your curb idle too low.

All are possibilities but EGR valve makes the most sense. It's famous for causing poor idling and/or stalling at low RPMS. Best of luck.
Greg