This hurts my brain.
If the engine isn't warming up properly it needs a thermostat. You said you replaced it, but what temperature did you replace it with?
1mpg is not worth the effort. Especially when you're talking about 1mpg "in town shopping" . We see 100 days over 100 here annually. The thought of pulling a mechanical fan from a 3/4 ton truck is beyond my comprehension. Worrying about 1mpg city in a tow rig tells me things: 1, buy another car for farting around town and use the tool as intended. 2, swapping to electric fans is great, especially if you add an overriding switch for when you know it's going to need additional cooling, but removing it altogether means something isn't right.
If you see that much cold weather why not just run a block heater? I've never needed one, but isn't that what they're for? Or maybe remote start?
Even on single digit days my 2008 5.3 truck was cranking (some) heat within 5 minutes or less.
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