2003 Ford F150 erratic temperature guage

I have a 2003 F150 with 145000 miles. The temperature guage has been ierratic,indicating a hot engine to the point of red lining. When the light came on I lost power. I pulled the truck over and checked engine and found that it was not hot I could put my hand up engine and felt no unusual heat, heard not ticks or noises indicating heat. I got back in turned the truck back on the guage went to normal and I drove another hour with gauge rising but not red lining. Since then I have driven the truck on the highway and had erratic temperature guage usually beginning at about 20 minutes into the ride. While I have had the guage climb into red line I have only had one other instance where I have seemed to loose power, I pulled over checked for a hot engine which I did not have, got back in the truck and had a normal reading. Throughout the trip the guage was erratic but did not red line. Also checked coolant during this time and was within normal levels.

Any ideas
Gary