Been a long time since I messed around with decoder so have forgotten quite a lot.
Test the motor on DC, connect power to the wheels first , then test on a section of track.
If it runs well on DC then there's an issue with the DCC decoder or CV settings such as starting voltage etc if its struggling the same section of track.
I'd start by resetting the decoder to factory settings (CV8 to 8 usually) which is usually sufficient to get most thing started.
The Stay Alive will work for dirty track but not if it runs well on DC already. Which decoder? Do you have the manual? If not, it may be online