my 13 does (did) have the thermal bypass. However before I removed the valve and installed a deep pan my temps towing a 15K 5er were always in the range your seeing now. 170-180 cruising and would get up to 220-230 on a cool-hot day towing in stop and go traffic or going slow thru the mountains. Would come down right away once cruising again. Thought these were pretty standard temps while towing
How are the temps now that you removed that valve?