Make sure your actually using a decoder and not just the DC analogue blanking plate that is provided with the loco. If so it will not run properly at slow speeds and the other functions may not work. Failing that.......,,Each decoder has a list of CV's. Each CV is assigned to a particular function. Each CV has a range of numbers that can be adjusted to set the desired value of an individual function, ie. acceleration, auxiliary lights etc. Check the CV list for your decoders on-line. Everything you can think of is usually adjustable, although more expensive chips have more functions. As a suggestion, I like to use the momentum function on my controller which is applicable to all of my decoders. This function provides very smooth starting and stopping even if I select a high speed. Regardless of the momentum function, you should be able to run at extremely slow speeds with DCC. Hope that helps.