Take Gun Runner John's advice and oil the journals. If you haven't oiled the journals, lately or ever, you might give each a cleaning with a good squirt of WD40, then wipe them down and apply oil. Then do what real railroaders do if a train is under powered - add more power. If you have trouble starting a train, shove back for slack and then try again. When you have bunched slack in a stationary train, your power only has to start one car at a time as the slack is pulled out.
If you have MTH Premier diesel locomotives, you can replace the rubber tired wheel and axle sets with solid wheels and eliminate the problems associated with rubber tires. Disposing of the tires also solves another problem: the illusion that you have enough power when you don't. If wheels slip, that's your indication that you need more power or reinstruction by the Road Foreman of Engines.
