Well they did fanny around with the datarate settings sometime ago, you may have to play with that again - been that long I have forgotten how.
Your best bet for all MorphXT related queries is the official emule forum
http://www.emule-project.net/home/perl/general.cgi?l=1
Go there enter the forum and register, a new section called mods will appear, in there you will find a subsection for Morph, post any queries there and someone should help you.
If Andu has finished his FAQ there may even be one at long last.
They are normally helpful there.