Nice to meet you.  Headspeed can cause drift problems but I don't think that's your case.  However, check belt tension.

I still fly a 401 on my B400 (FranKENblade 450 actually now) and it is very temperature sensitive. So depending on the season, the drift is different.  Try to let it set outside (out of the Sun) for a few minutes before you fly.  

I'm also a proponent of setting up in rate mode but don't expect to get it perfect (no drift in rate for 2 minutes+).

How bad is the drift anyway?

+1 on FBL