I have the 450 ISL, pulling a Ford Edge at approx 5K. Just completed a 3K trip through the mountains, NY, VT, PA, etc. lot of climbing and being from FL lot of flat interstate travel. FYI, tranny ran 204 max, engine 203 f., max. The range was usually both at 199 to 200 in 90 degree plus temps. I have seen many conflicting post regarding engine temps. Our coach is just breaking in at 17K after a great year of travels. I hope this helps, your temps sound a little low?
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Clay & Pebble
2012 Providence 42 M. Spartan Chassis, 450 ISL
Ford Edge toad, RM All Terrane, TST TPMS, SMI Air Force One, RVM95....