truck temptature went to 260 but was not over heating

You need to know what the real temp of the engine is. Buy a noncontact infrared thermometer device. Home Depot, Lowies, The Shack. Once you get one, measure temp where each rad hose attaches at engine. Should be no more than 10 to 20 degree dif.

This is very common on the 03-06 Silverados. The cause is the motors behind the gauges are failing, they all go out eventually. You can get it repaired here - www.drspeedometer.com and there's a DIY guide here - www.howtorepairmyinstrumentcluster.com