After changing my water pump my temp gauge doesn't work

My mechanic replaced my water pump due to a slight coolant leak. 2003 Chevy Avalanche 1500 with the 5300 engine. Replacement pump is an updated AC Delco facotry pump per the mechanic with a new updated thermostate. Following the repair the temp guage on my dash does not move. It stays on the lowest setting being 160 degrees. The heat works and the pipes out of the radiator are hot (can only touch for a second or so) but the temp guage does not work. I assumed that a wire or something for the guage was left disconnected but my mechanic says that with the change of the water pump there is nothing that would have been connected or disconnected in regards to the temp guage on the dash. He says the new pump is designed to run the engine cooler. I always thought an engine needed to run at 190 +/- degrees. Should my engine run cooler with the new water pump? Could there be something disconnected affecting the temp guage on the dash? Should I be concerned? Please advise. Jeff