A couple of comments.
If multiple units from the same manufacturer and having the same drive system will not MU, then one of the units has a malfunction. The slow unit probably has a bad motor or a misaligned gear system. The slow unit should be investigated/troubleshot.
Not all locomotives using the China Drive have the same gear ratio. While they seem to have the same motors, different manufacturers use different gears on the motors and the axles. I am just starting to investigate this, but I already know that K-Line diesels with the China drive run faster than Williams locos for the same track voltage.
I am currently investigating the differences between Lionel and MTH, with the intention of building a powered B unit to match my Lionel Alco PA. I plan to use the Lionel PB body and chassis, and power it with the drive system from an MTH DL 110.
