I have three locos lashed together pulling 18 empty wellcars. A C40-8, Dash 8 and a Dash 9 44cw. Plenty of power or so I thought. The speed limit is set at 70mph but they can only reach 55 mph. Yes, it's level for the most part. There are 3 different engine specs involved. Could this be the problem? No problems with signals or switches. Any ideas or suggestions? Thanks.