90c on the highway is normal. Mine runs that in the summer with the AC on. If it only is running warm on the highway it sounds like your radiator is getting clogged. It might be a good idea to take it out and clean it up a lot of crap gets stuck in it.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200