Do the joined movies play smoothly on your computer? Just to make sure if it is the problem of the movie or the PCH.
I got to know TSSplitter would join some files without re-encoding, but it does not support the .m2ts files from camcorder or Blu-ray (stated on official site).
You may also try Final Mate, which also join m2ts files in native format. It imports m2ts files from camcorder, but not BD.