Hi again everyone,
First of all, thank you for all the help, ideas, and supportive approach with this. Although I have played with DCC before, I had never taken programming beyond address and direction change. Tonight I had to 'bite the bullet' and start playing with CV settings. The bad news was that some of the setting suggested here made no difference. I then reset the chip - again, no difference.
Now, the good news; I found the following thread:
http://www.rmweb.co.uk/community/index.php?/topic/45821-Bachmann-36-553-decoder/
There was a post on there about back emf and the relevant CVs; this 'rang a bell' in respect of something I had seen elsewhere (but now cannot find). I changed these as follows, based on suggestions from Bachmann about the Std cl4 2-6-0 - CV 54 to value 12, and CV 55 to value 63. What a difference! Crawls gently and smoothly; there is no erratic speed change, noise, and it performs equally well in both directions.
82021 is now back in its box however I did forget to deal with the analogue running. Ah well!
Thanks and regards,
Alex