OK, so I went to Pep Boys and bought this little PT Diagnostic Scan Tool (W2977) for 20 bucks. It's really just a code reader, but it erases and re-sets, so it's better than nothing...until I learn what I am doing.
So I plugged it in and followed the directions. I was half-expecting to see a BUNCH of codes pop up, because I've only had this Tahoe for less than a month, and who knows what kind of issues could be lurking, right?
YES! Just one code...P2135.
The booklet only goes to P0999, but a quick search on the internet confirms it has something to do with the TPS...could be a faulty sensor, or connection, or ground or bad throttle body itself. Also, good to know that you don't have to replace the entire throttle body, just the sensor, if it's bad.
I've been driving around ever since I had the issue, and it has not repeated. I guess when I turned off the motor, waited awhile, then turned it back on, it somehow rest itself? The CEL is not on, and the DIC message is gone, but do I need to erase the code with this little PT reader Tool?
It's not by any means a complete scanner, but I'm glad I bought this little reader to keep in the glove box.