Are the U.S. Topo maps, specifically the U.S. 24K topo, compatible with the 3597LMTHD GPS unit? I ask this because the topo descriptions don't list that specific GPS unit. Not sure if that means it's not compatible or perhaps it was just a new model and wasn't added to the topo compatibility list. Anyone know? Are topo maps compatible with the 3597LMTHD GPS unit? Thanks