If your eyes are on with all the different hoppers you've tried I'd suspect the paint. Also dumb question but did you try a new battery/ check the voltage? Btw most tm guys will yell you to throw out the lube that came with it, try some sleek lube oyster TechT's gunsav.
With my TM15 and TM7, the only time I have broken balls is when I am using cheap paint. I have read some where that also a bore issue can cause a problem. what is your rate of fire when you break the balls? the reason I ask is if your break a ball in the barrel not the breech it is possible the first ball is getting stuck in the barrel and not cleared when the next ball is shot and hit the first ball and breaking. A higher rate of fire will cause this to happen more often. I could be wrong.