Ed,
I was having problems programming the MRC sound decoders that came with the Athearn Challengers and Big Boys when they first came out.
After doing a bit of research, I bought and installed a Soundtraxx PTB-100 Programming Track Booster, and all my problems disappeared.
It now resides on my portable power board for my layout for use on the programming track, but I've gotten rid of all of the early MRC sound decoders and replaced them with Tsunami's.
If you don't have a programming track power booster, the PTB-100 has an excellent reputation, and will solve your MRC sound decoder programming problems.
Cheerio!
Bob Gilmore