Thanks for all the responses. I pulled the shields back and there is in fact a small factory transmission cooler in front of the AC and radiator. I didn't see any external obstructions, but I gave all the coolers a good blast of water to make sure they are clean.
The radiator was leaking when I looked at the truck on the lot so they had to replace it. So at least I know the radiator and dexcool are new. But I'm wondering now if the external cooler might be partially plugged internally. Tomorrow I'm going to warm it all up and then run my hand across the cooling fins and see if the cooler is even getting warm.
I'm thinking about what BenK said about the fan clutch. But the radiator doesn't run hot. It stayed at 195 the entire trip so would a fan clutch still help?
As far as the fluid flush, well that ship has sailed as I had the fluid changed when I bought it last month. The old fluid didn't look too bad so crossing my fingers that the was minimal or no varnish buildup.
As far as the work truck transmissions failing around 100k. Yes I've heard that about the 4L60 and talked to the local transmission shop when I bought my original Suburban. Their recommendation was to avoid the 1/2 tons with 4L60's and go with a 3/4 ton since they come with the 4L80 which is supposed to be much more stout. It was one of the reasons, but not the only reason that pushed me into a 3/4 ton.
It could be as Grit Dog says and it might just be more worn out than I thought. All I can say is I hope not on that front as I need it to last a couple of years before I think about buying something different.
