5.3L Flex Difficulty Holding Operating Temp?

[LastFbody]

I have an 03 Tahoe with a Z code 5.3L, and I'm just wondering if its normal for these engines to have difficulty reaching and maintaining operating temperature (just below the 210 mark) or if it's just my thermostat being stuck in the open position.

It has no real issues spring/summer/fall other than it heats up somewhat slow, but it stays at operating temp once it gets there. Winter is a different story, depending on how cold it is it sometimes wont even reach that 210 mark. Usually it eventually gets up there, but then driving at high speeds with the cold wind brings it back down to the 160-180 area.

Edit: I'm running plain old 87 octane gas, not running E-85 unless it gets super cheap

 

[Metaldrgn]

It does take a little longer to get up to temp. I've driven mine in -14 but it still gets to 200 unless it's just idling

I think the thermostat would be most likely if it isn't heating up all the way at high speeds.

 

[LastFbody]

Yeah it definitely wouldn't be able to get up to temp in -14. I would imagine it's been stuck open since I've had the truck Oct 2012-Now, but it hasn't been such a glaring fault until this harsh winter. My heat has always been anywhere from marginal to passable, especially when compared to the 2002 Silverado 2500 6.0 I sometimes plow with. That could be a somewhat unfair comparison (not sure), but thats the only other similar-era GM truck I've had any real experience with.

Question 2: Do these trucks inherently have inconsistent mpg, or is that another thermostat issue? I can usually pull ~20 mpg highway @65-70 mph but other times its as lousy as 15 with a headwind. Does a headwind affect it that much with aerodynamics by itself?