This last weekend we went over hwy410 near Mount Rainer, and the bloody truck overheated on us 2 times going east and once heading west

. We were pulling our 3horse trailer with 3 horses in it and it started to overheat, and the trans temp light came on as well. The truck is a '94 3/4 ton 4x4 with 320k miles on it. Could the fan clutch be shot? or the radiator be plugged up internally or externaly? or do I have more troubles that I don't know about? This is the first time that I've ever had any problems and I'm kind of dumbfounded

. HELP PLEASE.
Thanks and have a good day