Every car I've ever had w/ remote start (unless we're talking back in the '90's in highschool w/ a beater cavalier) - will shut down after about 20 mins as you stated. There are numerous reasons for this - protecting warranty/hard parts (idling for days on end in the event the truck is accidentally started w/ a full 36 gallons in the tank), keeping from filling up a closed parking area/garage w/ carbon monoxide after inadvertently starting a vehicle and/or forgetting to shut it off, not pissing fuel away for no good reason - call it environmentalism or whatever its just a waste.
When my dogs in the car if its 80 or under shes just getting windows open & her bowl of water & I will park in a shaded spot, over 80 shes either coming w/ or I'll leave the truck on w/ keys in it & AC on....now that I think of it couldn't you just lock the truck w/ the keys in the ignition & AC on then unlock it w/ the touchpad when you return?
Truck will attempt to shut down even if you are sitting in it with the key, if it is idling and not moving. It prompts that a shutdown is about to occur, and you can cancel the shutdown if you wish.
FROM THE MANUAL.
Automatic Engine Shutdown
If your vehicle is equipped with a keyless
ignition, it has a feature that automatically
shuts down the engine if it has been idling
for an extended period. The ignition also
turns off in order to save battery power.
Before the engine shuts down, a message
appears in the information display showing
a timer counting down from 30 seconds.
If you do not intervene within 30 seconds,
the engine shuts down. Another message
appears in the information display to
inform you that the engine has shut down
in order to save fuel. Start your vehicle as
you normally do.
Automatic Engine Shutdown Override
Note: You cannot permanently switch off
the automatic engine shutdown feature.
When you switch it off temporarily, it turns
on at the next ignition cycle.
You can stop the engine shutdown, or reset
the timer, at any point before the
30-second countdown has expired by
doing any of the following:
• You can reset the timer by interacting
with your vehicle (such as pressing the
brake pedal or accelerator pedal).
• You can temporarily switch off the
shutdown feature any time the ignition
is on (for the current ignition cycle
only). Use the information display to
do so. See Information Displays
(page 113).
• During the countdown before engine
shutdown, you are prompted to press
OK or RESET (depending on your type
of information display) to temporarily
switch the feature off (for the current
ignition cycle only).