Don't know why a GPS would want to divert anyone from taking on the Icefields Parkway, I would certainly ignore it.
As others have noted, the route is prohibited to commercial traffic such as semi's and such - however you will have a number of motorcoach and tour buses on the route....class A RV's are permitted.
A valid park pass is required for permitted entry on the Icefields Parkway.
Out of all the routes I driven on, this roadway to me is the most scenic and majestic in all of North America....Driven it in 2011, 2012, and 2013 and would have driven it in 2014 and 2015 if it weren't for turning around on the way there due to mechanical issues and minor health issues in 2014 and just mechanical issues in 2015 (5 days behind schedule as that would take all the extra time to spend in the Canadian Rockies to enjoy).
Do NOT miss this gorgeous roadway and if possible drive it in both directions upon your visit !