In 2012 we went up through Banf and Jasper and came back down the Cassiar in our 37C PA pulling a Ranger pickup with no problems. You can't pick a bad road for animals and scenery. On the way South we came across the Taylor and Top of the World to Dawson City. That big V-8 will pull you up anything you will encounter. Use the Allison braking feature down the grades to save your brakes. Definitely recommend supplemental brakes on the towed and take it slow and easy going down the grades.
Ditto on the reference books mentioned above.
Have an enjoyable trip and post your results when you get back to AZ.