I love my Jimmy and have been driving it for many years. It has typically run around 150-160 degrees at all times. Recently it overheated and I had the thermostat replaced. I asked the techs to give me their opinion on the water pump and they said they thought it was in good shape so they only replaced the thermostat. Since I've been driving it again, it has been running up to 210 and beyond on relatively short trips around town. Could this indeed be the water pump failing or is there something else I'm not thinking of that could cause this change in running temperature. I appreciate any insights. Thanks.

Does it get in the red? What temperature rating was the thermostat you replaced? Sometimes they give you a higher temp thermostat.TAke the radiator cap off and watch the flow after it warms up and the thermosat opens.IT should be at more that a trickle.Flushing the radiator might help.Make sure the fan shrould is in place.Wile running hold a cigarette about 6 to 8 inches from the radiator if the smoke goes in well when the fan is turning you are good there.last thing on my off the top of my head list is a head gasket if all else fails get a compression leak test done to see if there is a head gasket leak.I hope this helps.Good luck and letus know how it turns out.

Have you checked the fan clutch ? I had one go bad a few years ago and experienced similar problems. It should have some resistance when you give it a spin with your hand(turned off of course :-)) and can be heard while the truck is running hot. Hope this helps.
SEDIVER