I'm not knowledgeable in TT matter, I hope someone else will read your post and reply here.
Concerning Garmin, new models have fast processors and draw the map fast, zooming in and out.
Autozoom:
If the zoom level is set to "Auto", it is displayed as "Garmin" thinks is best., if you like you can disable it in maps Settngs.

If you like a super moddable software try iGO on your Android phone.