Newbie having problrems with cars unhooking.

I'm a newbie with an N-Scale Layout and on advice from others all my cars are converted to Bettendorf Trucks (the ones with the little copper wires).

Problem I'm having is, I an incline and it has a cure. My 40' boxcars seem to come unhooked when they reach this point. My 50' seem to work fine. This happens with several cars.

I suspect it is a problem with adjusting the wire length but I'm not sure. I'm not even sure these trucks are the best way to go or if I'm even installing them right. They seem to float and are not sitting firmly on a couple of the cars.

On another note, I have an approximately 30' tanker that seem to need weight, when I strap a penny to the bottom, it works perfectly. otherwise it's off the track at the first bump. Any way to weight it down with something more appealing to the eye?

Thanks, Mike