Supposing that the combination of parts is compatible (I’m sure there’s a chart somewhere but I don’t know off the top of my head), how’s the cage angle looking? The height? Is the problem shifting in both directions to the middle or in one direction?
Triples are pretty fussy about the shape of the mech cage, so you're unlikely to get good results using a completely different mech.
Especially if you're trying to use a double-specific mech on a triple.