Give it time.
I'm averaging about 19 back and forth to my two-light town and 22-23 on the highway at old-man speeds. I noticed a drop with winter fuels.
For me–where I live–it would be a waste of money.
For your situation, the $60 might be worth the peace of mind. Maybe I missed it, but I'm surprised they didn't use security torx heads and include a bit for installation.
You'll not get much bang for heat from a battery system. I've got a teardrop camper with a Propex (propane) heater. It's flat-ass wonderful and uses very little electricity.
But they aren't cheap.
I'm not connecting those GM dots to turbocharging. The reason turbos have a mythological reputation for unreliability is that back in the 90s, there were aftermarket turbos sold for engines that weren't designed for turbos.
The remote start via the app uses cell connectivity. If the phone isn’t within Bluetooth range, it can’t connect.
It’s an easy fix once in the truck. Just hold the volume knob in until the screen reboots.