I have only seen the guts of these reels once but have you got the washers in place by the drag spring properly? I seem to recall having to disect one fishing last winter there is to be a washer on either side of the drag spring? The one on the inside will be buried down in that 'housing' and then one on the outside.
Not sure it could be the problem with maybe some slipping but is the cork on the reel dry or have you oiled/lubed it?
BTW.....is it the TMX4 or whatever that model was called?