Trains made out of any type or types of carts seem to lose speed extremely rapidly when traveling e-w or w-e. I can stack up 15 booster tracks and the train will still come to a halt 3-4 blocks from the boosters. South-north traffic is unaffected. Carts alone work in all configurations.

Tested on minecraft 1.4.7, forge 6.6.0.518, railcraft 6.14.0.0.

Oops, that supposed to apply to both directions. Accidentally applied it to X and Y instead of X and Z. So don't worry, North-South will be slowed as well in the next release. (But only if the Locomotive Module is enabled)

Hmm so if I understand it correctly, it's not possible to run trains using only booster tracks any more, if I have Locomotive Module enabled ?
Hmm sorry, but maybe it would be a good idea to mention it on the wiki somewhere (at least in the Version History) I was just going to report the same problem here, because I didn't find any info about this on the wiki.
Is this be turned off by parameter in the config file ? Or do I have to disable the Locomotive Module completely to revert back to original behavior ?
Thank you

You have to disable the locomotive module completely, and there is no change log because it was accidentally added to the wrong version.