20 mins is lots.
Just a few comments on the past posts without attaching them to this posts.
Oil pressure and OP switch.
Having great oil pressure is not a symptom of a faulty switch, a bad switch (or an open wire at the switch) will read zero, but the engine is still providing proper pressure.
I had a bad switch on my '05 Envoy, the pressure reading would drop off to zero and, the PCM thinking the real pressure had dropped to zero would turn the truck off; but, only after the truck was stopped and the pedal was at idle (I assume to ensure you were not in the fast lane of the freeway).
It is an easy change.
Stepper motors may fall off to zero and stay there; but usually, as Voymom said, they find a new zero and bounce around from it.
The rough idle may disappear when the plugs are changed (96,000 is longer than I like to leave them in there), O2 sensors wear out as well, have it (the front one) changed when the plugs are changed. Also, a good time for a new air filter (and if an '02 to '04 truck, a new fuel filter as well).