Overheating & Transmission issues on 2007 Chevrolet Uplander

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1) My 4 speed automatic transmission often doesn't drop back into first gear at red lights & then it kicks like hell when I drive off.
2) At fast highway speed or local on a hot day the Temperature guage & the computer indicate overheating -- but it seems it is NOT really!
Any comments / Advice / Similar Experience?
(1) Answer
I have a 2006 with similar overheating issues. Usually in the morning, within 5 miles of my house, my temperature gauge will spike and I get the warning " Reduced power,pull over and shut off engine when safe". If I turn on my heater, it will only blow cold air. I can remove my radiator cap and it is not boiling over. Both it and the reservoir are full. I originally replaced the thermostat thinking that it was sticking. This worked for about 2 months.
Did you ever find a solution?