I have an ’89 Blazer that is stock and the motor has nearly 200k miles on it. My brother gave it to me with a bad transmission. I have fixed that with a 700R4 from Bowtie Overdrives and I’m now running a trans temp gauge and a trans cooler behind the radiator. Tires are 31” BFG ATs and the diff is a 3.73. Around town (45 mph or less) the truck runs very cool. Engine temp is below 175 and the transmission oil is pretty consistent at ~150 degrees. I’m usually running in overdrive turning 1000 – 1500 rpm at these speeds. On the highway things are not as good. Driving 65 – 70 mph, I’m turning north of 2000 rpm. The engine temp starts to creep up to 175 and the trans temp is usually between 150 and 200. Any sort of hill and the engine temp goes higher, 185 or so, and the trans temp hits 200 or a bit above this. I live in Seattle, and it is not hot here. Ambient air temps are 65 – 70 degrees for the readings quoted above. My concern is the transmission temp. I would really prefer it stayed ~150 degrees in the pan where the temp sending unit is. My current thought is that the radiator is going bad. What do you guys think?