Be sure your build report is set to the most detailed version.? That report will tell you what cars were considered and what cars were rejected.? There is a reason and it is in the build report.? If you have a particular car that you think should have been selected, search the build report for that car and see what it says.? It is also possible that the program could not find a destination for any more cars of the types remaining.? You can also try building that train in aggressive mode.
Dave...
David Cochrun