Chevrolet Repair: Overheating, upper radiator hose, coolant temp

Question
91 s10 with 4.3 engine temp gauge goes over 260 but no hoses blow or any other signs of overheating. Replaced thermostat and still have same issue water pump doesn't  have any leaks and oil looks fine. What could be causing this

Answer
GOOD DAY LEE, WELL FIRST THINGS FIRST,IF THIS ENG IS REALLY RUNNING AT 260 THIS WILL CAUSE DETRIMENTAL HARM TO THE HEAD GASKETS AND HEADS AND POSSIBLE BLOCK....SO WITH THAT BEING SAID WHEN THE GAUGE IS SHOWING THIS CAN YOU SQUEEZE THE UPPER RADIATOR HOSE OR IS IT HARD AS A ROCK..IF THE UPPER HOSE IS WARM BUT NOT REAL HOT AND HARD I WOULD THINK THAT THIS ENGINE IS NOT REALLY RUNNING THIS HOT..WE HAVE TO BE SURE BEFORE WE CAN DO ANY OTHER DIAGNOSTICS.  SO THE ONLY THING LEFT IS A BAD TEMPERATURE SENDING UNIT OR THE GAUGE ON THE DASH IS LOOSING ITS MIND..YOU COULD TAKE IT TO A SHOP AND HAVE THEM PUT A TEMPERATURE GAUGE IN THE RADIATOR TO BE SURE IT IS NOT THAT HOT. THIS IS A FAST WAY TO TELL OR YOU COULD HAVE THE TRUCK SCANNED WITH A SCAN TOOL TO CK FOR A COOLANT TEMP SENSOR READING,THIS WILL BE DIFFERENT THEN THE TEMP GAUGE THAT THE GAUGE GETS ITS REFERENCE FROM..IF THE SCAN TOOL SHOWS THAT IS REALLY RUNNING THAT HOT THEN YOU HAVE A PROBLEM...I WOULD THINK THAT IF IT REALLY WERE RUNNING THIS HOT YOU WOULD HEAR THE INSIDE OF THE RADIATOR MAKING ALL KINDS OF BANGING NOISES...IF WHEN THIS GAUGE IS SHOWING THIS HIGH TEMP AND YOU CAN [SAFELY] REMOVE THE RADIATOR CAP AND THE COOLANT IS NOT BOILING OVER WHEN THE ENGINE IS RUNNING I DON'[T THINK IT IS THAT HOT..LET ME KNOW WHAT YOU FIND AND IF YOU NEED MORE HELP GET BACK TO ME.
GOOD LUCK TO YOU,,,,TOM