It sounds like a problem I had with mine, it would go up to 260 though. This was with a new radiator and a flush. It turned out to be the impeller slipping on the water pump(junk rebuilt). Now I have a NEW water pump and 210 is the hottest it will run even in 95 degree traffic! The fac. cooling system for the 4.3 S10s is more than adequate when its working properly! Also the POS pump would "gurgle" air into the system that you could hear when you started the engine! NOT GOOD! I have pulled a 16' 2200# horse trailer with my truck thru hilly sections with no problem and NO Trans-cooler. Never tow in O/D and yes, a trans cooler is a good mod. for under $70 in most places.
1989 GMC S-15 4x4 4.3L/700R-4, 3.08s, 31" Sport Kings For Sale
1985 S-10 4x4 Soon to have 3504BM/TH350/D44/14FF, 35" Boggers