2001 Cadillac DTS STARTING

Have you done a relearn on the pass-key?
GM PASS LOCK RELEARN- Ignition to "run" position, try to start and let key return to "run" position
Approx ten minutes security light will go off
Turn key "off" and wait 5 seconds
Repeat 2 more times for a total of 3 relearns.
Turn key off, then start it

To get a better understanding, when you say "feels like it's going against nothing", does it sound like the starter is not engaging the flexplate, or the engine is turning over with no compression? Do you try this one time and wait an hour, or several times and then wait an hour. The aforementioned pass lock relearn would not be intermittent in nature. I would first start with checking to see if the starter is getting a signal when this is happening. If you can provide a bit more info on the symptom. I have, in the past, had a sticking oil pressure regulator that causes max oil pressure and creates a no compression-no start, have also had starters that spin but don't engage the flexplate.

I dont know about the passlock not being intermittent, I work with some one who's chevy was intermittent.

A pass-lock fault could be intermittent. A re-learn would most likely not correct a pass-lock fault.

That may be true, they ended up cutting a yellow wire to the system.