Overall, I'd say poor driveability, maybe surging or loss of power at higher rpms, often the idle will wander.
Sometimes it's hard to tell where oil is coming from so, if you unplug it and spray cleaner on the plug & sensor to clean it you can then recheck for the presence of new oil leaking through
the sensor (a sure sign it's failing)
The nice thing about diagnosing an ICP problem is that when unplugged, the PCM will default to a limp setting and allow the truck to run without it. If that improves your symptoms you have a good idea as to it's condition.
BUT all-in-all they're an expensive thing to just "buy and see" so, a good scanner will eliminate any questions.
cj45lc - not enough oil will come out to worry about