TMHippo: I had this happen to me earlier this year after I cutt the comm on my MVP. The problem with mine was that after I cut the comm I forgot to clean out the slots between the comm segments. This leaves piles of copper in the gaps that can cause the brushes to short across two segments at once.(bad thing) Just take a hobby knife and get that extra copper out of the slots and that should clear up you problem.
If thats not it, then I'm not sure what it is other than a speedo problem.