*UPDATE* problem solved!! Coolant temp on hills GMC 3500

On long hills the temp goes to 210 but on the down hill goes back to 180/190. When mine did hit the red I had a flush done, that did not do it had the thermostat changed, that did not do it had the fan clutch changed bingo. Recently the breaks went and due to rotten break lines on the power steering/break pump. garage replaced the pume and installed an after market cooler and everything is perfect. good luck 235 degrees your engine is calling for help. escpecially if it does not recover quickly.