Can you use a rock to pound a nail into a wall stud ? Sure can but a hammer is the right tool for the job.
Can you use a butter knife to screw in a screw ? Sure can but a screw driver is the right tool for the job.
Can you pull a big 5er with a gas motor ? Sure can but a diesel with all it's torque and power is the right tool for the job.
Especially when you are running around the west coast in 100+ degree temps. and pulling long, steep grades.
The new diesel trucks cost more but one thing is for certain when you are loaded down on a long trip you can leave your worries as far as your equipment home when your 5er is hooked to a high torque diesel !! Ever see any of the guys towing 5er's , TT or any other type of trailer for a living using anything but a diesel pickup ?
Good luck with what ever you decide to get.