Route numbers may be used if the route doesn't otherwise have a name. And sometimes the route number is shown on the screen but not spken (or vice versa).
We use the 2797 in the Toad, but have the Dezl 760 for the motorhome - I like being able to enter the dimensions of the rig (height, length, weight, etc) and get some assurance that I won't be routed to places that won't be big enough. The Dezl is essentially a trucking unit, but with RV pofiling built in. Takes some getting used to, but hasn't done us wrong so far. Although why the unit insists that the exit ramp to a rest area or truck stop has "unknown truck access" is beyond me. :)
al