I have the gauge problem, it is either a bad connection like you said, or in my case and some others, a bad and/or corroded ignition switch. Ignore it unless it becomes consistent.
Never flush a transmission. Some people will say there are exceptions, but even if there are, the safest thing to do is to drop the tranny pan which will drain almost half of the old fluid out, replace the filter, and refill with clean fluid. 97-03 should use a Dexron III equivalent, 04+ either Dex III or VI if you'd like to try it at your own risk. The Dex VI actually lowered my 05's tranny temps a bit.
Get a Transgo shift kit if it slams between gears. It's a bandaid fix, but it will prolong the life of the transmission either way and will usually get rid of violent gear shifts. The usual culprit is the PCS solenoid, but it's located behind the side cover and costs a lot in labor. Only worth it as a DIY project.
I also have the occasional power loss. A restart fixes it every time. I'm almost certain at this point that it's transmission related, as in that stupid PCS solenoid.
