Sounds like you may need a different track and roller cleaning procedure. I run a lot of the little motorized units. They are finicky about switches at times, but in general I don't have a lot of issues with pickups. I have a number of the small K-Line based units, and for those I try to add rollers if possible. A typical example is this Porter TMCC upgrade.
I added a roller to the little coal car to solve the roller spacing issue, and did a copper strip to increase the outside rail connections as well.
I also have this clown car upgrade with TMCC & sound, I ganged the two together to benefit from four rollers and eight wheels for better track contact.