Makes me wonder if the problem is the trucks or the trackwork itself.
I use sprung trucks exclusively (mostly Kadee, but there are a few Old Pullmans in there, too), and they stick to my rails like glue (maybe I'm the one with questionable trackwork? Then again, my steamers NEVER derail, so it can't be all that bad).
Although the cars are WAY too light to compress the springs, the sideframes will twist a bit relative to, and independent of, each other, allowing the wheels to follow any irregularities in the track. A rigid-sideframe truck does not do that - as the wheels roll over track irregularities (like frogs, etc.) you get the short table leg syndrome. Sprung truck sideframes move enough to prevent a lot of that.
Then again, I've had little experience with metal wheelsets in rigid trucks. I had the plastic wheel rigid trucks (Athearn) when I decided to try sprung trucks with metal wheels. The sprung trucks tracked so much better that I changed everything over and never looked back.
Now, with the exception of three old Roundhouse ore jennies and one very old Varney gondola whose trucks I've never replaced (which cars make up my work train, one jenny carrying spikes, another track nails, and the third picking up the ties I cut off the ends of the flextrack to allow the rail joiner to be installed. The gondola carries the rail joiners), no freight car hits my rails until it has sprung trucks.
