they have changed a bunch of small things that i had trouble with on the dc30's. they are on dayglo type collars so you can now run an ecollar and dc40 on one collar, have longer whip style antennas, everything is inside one unit now instead of having the wires running up to the gps part.(it's all one piece), the best part is the charging sytem, they now have charging cradles that just snap in place much like a tritronics charger. i have only been running the dc40's for about a week now so i will keep you updated. it was a "no-brainer" for me to upgrade since they addressed all the issues i had with th dc30's
