"The CEL has not lit up with any codes, and when turned to run position it does in fact light up."
This is good.
"I checked the cat out based on a post i read here last week where you put your hand over the tailpipe...check for pressure."
Hmmm, it might be better to try removing a O2 sensor to see if it performs better if you are testing to see if the cat or precat is plugged.
"If the CEL is not lit, can I still retrieve codes?"
Yes, if there is an intermittent code.
