2002 Ford F-250 A/C quits cooling

A/c will stop cooling and then start coolong on very warm days, have cleaned core good and verified that I have good air flow, check pressure and all is good, when it is cooling it will bring vent temp down into the 55 degree range, and cold side will sweat all the way back to the compressor. Have had the fan clutch replaced at 100,000 miles, is there a way to test it, or the high pressure cut out switch.