locomotve speed control

[Karl S]

I'm relatively new to model trains. I have a couple of 4-6-0 locomotives that I bought new on E-bay.
After several hours of operation I noticed that both engines were not running as fast as they did initially. I cleaned the track thoroughly thinking that  was the cause but it didn't make any difference. I also cleaned and inspected the locomotive wheels. Nothing seemed to make any difference. Can any one tell me what the possible cause may be?

[p51]

If they're both doing it, I'd look to whatever you're running them with. While it's possible for two locos to have the same problem at the same time, it isn't likely.

[Karl S]

I should have mentioned that I also am running a 4-4-0 that is new and it runs fine. I have noticed that one of the 4-6-0 will try to creep even when the EZ DCC control is at zero.                     

[H K Cole]

I have some bachmanntrains engines with dcc, do they have cvs5 &6 where you can make them run together with each other or different makes of engines