I use an 18 needle now. 16 was working for me, until I broke one
I think I mucked the timing a bit, because after that my 16 needle was just like you - thread breaking all the time, and skipping stitches when moving towards the back. Prior to the breakage I had some issues, but infrequently.
But going up to an 18 needle solved ALL my problems (phew) so I don't need to have my machine re-timed after all. Three quilts completed now (since then) without a single thread breakage or skipped stitch. By thread is Golden Threads Quilters Choice.