I had the same problem happen today on my 92 Gmc sierra. It turns out the harness clip on the Coolant Temperature Switch snap off due to age I suppose. Anyway, I connected it and secured it until I can get a harness connect replacement (which for some reason is rather high in price for what it is). Cranked it up and took it down the road and the gauge works, it isn't loosing power when I come to a stop (it had stalled completely a couple of times earlier this morning), and I still have a little eratic shifting cause my tranny needs to be replaced. Ironic the same symptoms and problem here...wow. My radiator hose actually constricted a couple of times too. I constricted from the thermostat neck all the way to the radiator too.
Lee