Above is the link that saved my sanity today.
At 100,000 miles on my 2007 Avalanche 1500 LTZ, I got the idea to clean the MAF sensor & TB with dedicated cans of CRC cleaners at a cost of $11.00 total for both. The hunch was that dirty above items would lead to spongy pedal response, drifting idle, and harsh light pedal shifts
During the TB cleaning, I was too lazy to disconnect the plug and accidentally gave it a good 360 degree+ twist.
The outcome was still- harsh low RPM shifts and random idle at 600, 1100, 1700, or 2000 RPM.
I installed a new pigtail TB plug harness and followed the relearn idle procedure at that link and has improved. 600 RPM idle and reasonable shifts are the rule now.
Just thought I'd share.