Loco slow on DCC compared to DC

Compatibility is not the issue. Both items are DCC standard.

The number of speed steps makes no difference. The same pie (total available speed), just more slices. 128 steps only gives you a finer degree of control.

 The speed of the loco is determined by the track voltage and the design of the locomotive drive train. It may have lower gearing or just a poor design.

Check your track voltage. It can be hard to measure the DCC track voltage accurately since it is a PWM digital square wave. 

You should be getting about 13.8v AC on the tracks for HO Scale. The actual number does not matter as much as getting the SAME number everywhere you check.

Voltage drops, especially with the loco running, might indicate issues with track bus wiring that need to be improved.

also check out www.wiringfordcc.com

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 Slow moving locomotives can be from a couple of possible reasons:

1. Lack of proper layout wiring. For HO scale you need track feeders every 6 feet, for N-scale every 3 feet. All track feeders need to be connected to a 14 or 12 guage track bus wire which is then connected to the Power Cab Panel.
2. Using sectional track. The use of sectional track introduces multiple electrical connection points that are prone to failure and have very poor electrical characteristics. If possible solder the sectional track together leaving just a few unsoldered for expansion joints
3. Dirty track or dirty wheels. Lack of maintenance can cause issues with DCC even more than under regular DC.
4. Decoder in locomotive needs to be reprogrammed to factory settings to clear out incorrect speed settings.
5. Lower track voltage. It is not uncommon for a locomotive to run slower on DCC as compared to DC. Standard DC power Packs typically are 15 volts or even higher. While this is impressive from speed standpoint it is NOT realistic and can even damage some locomotives. In DCC we focus on realistic speeds, better control and slower but very smooth movement. Under DCC track voltage is limited to 14v maximum. 12v for N-scale.
6. Defective locomotive or DCC decoder.