Also, the hybrid-specific parts are more costly, because they were specialized / lower-volume. Things like the power steering reservoir on the GMT800 (Silverado 1500) hybrids, for example (they probably used the BAS (alternator stop/start)). You can see the difference on those in the service manual. Take a look on Rock (as an example), and compare similar parts between the regular and hybrid trucks.
And as Moose said (and you're aware), the transmission is a unicorn. Finding someone to do major service on it... might be tough, outside of the dealer. And I didn't know it was a CVT. That alone would scare me away. I had a (non-GM) car with a CVT once, and would not want to repeat the experience (yes, different tech than the 2-mode GM trans).
Think about why those got a 6.0L, even though they were 1500 / half-ton... they had a LOT of extra weight to manage. Given the MPG penalty of the 6.0L over the (normal) 5.3L, you know GM would have used the smaller engine, if it were 'enough' (or else, they put it in to help 'sell' the hybrid, since you could only get that engine in a HD-rated truck or SUV (or a Caddy). One or the other, I'm sure.
I don't know whether they had AFM, but if they did... it would probably be calibrated more aggressively than the same system in a non-hybrid.
As one who earlier had three (!) non-GM hybrids in the family (two for me, one for the wife), I can attest to the mileage / weather issue you brought up (although, to an extent, that's true for any ICE-equipped vehicle, either with gas *or* diesel. They're just not as thermally-efficient in (really) cold temps (and fuel is reformulated to burn more readily in winter temps -- which hurts FE, vs. in the summer months. It's just not as apparent, because 'summer blend' has more ethanol (and fewer of some other compounds), masking what would normally be improved FE, vs. winter blend).
And, yeah... once it comes time to replace the traction battery... it's gonna be expensive, to the point where all of the fuel savings you accumulated are lost on the pack replacement. There's one brand that doesn't suffer as much from this... Toyota, with their HSD, which have packs designed to go up to 200K mi., and often go about 50K longer, before dying. Even then, it largely depends on your driving habits (which will likely need to change), in order to come out ahead, money-wise. Which leaves the 'environmental' factor -- and some will posit that the extra outputs necessary to make the car, add more pollution than the car will negate, during its lifecycle.
Hybrids were a nice bridge technology... which I bought into, for awhile... and I actually also liked GM's strategy with the Volt (where the engine was there only to replenish the electric propulsion drive). But 'full' electric is where things are going, and quicker than I'd have thought, too.
BTW, as an aside... GM and Honda entered into an agreement a couple of weeks ago to produce BEVs together (I think four new ones, two for each of them). Honda styling with GM underpinnings (GM's battery tech is really strong, I hear... must be, IMO, if Honda decided to throw in with them on this, although the two companies already had an established relationship, and get along well together). To be built in GM plants, IIRC (no NUMMI joint-venture plants, like GM / 'Yota did a couple of decades ago)
TL; DR: If you want a GM full-size truck / SUV, no worries -- IMHO, they do those vehicles very well, compared to their competition -- but I'd steer away from their full-size hybrids of that era, if you're risk-averse.