A route is always calculated; by placing the waypoints correctly and using a sufficient number of them, the route will match the planned route exactly—provided the correct map is used and the planner's settings align with those of the XT. It makes no difference which GPX format you use for the Zumo—GPX 1.1 (the standard) or GPX 1.2 (MRA's proprietary version). GPX 1.2 is transmitted as a route track with waypoints, so you need to include a certain number of waypoints in your route (up to a maximum of 28). If you do not wish to use waypoints, use GPX 1.1 instead.
And as previously mentioned: disable recalculation for planned routes, make the track visible, ensure you are positioned at or near the route's starting point, and make sure your Zumo has a connection to at least three satellites.
It really isn't that difficult...