Tahoe Limited "Thinks" engine Temp is High

[scumpoozie]

Hi. Bought a 2000 tahoe limited 5.7 and im concered about a few issues. One being the temperature. My mechanic put it on the computer and the truck is running at 188 F. When I bought the truck, the temp guage displayed about 140 F. I've chaged both temp sender units and the thermostat. NOW the guage displays 250 F plus. I've driven 200 miles with it "overheating" (according to guage) and truck never acts like it's acutally overheating. Any help is appreciated. Thanks.