Have you ever considered increasing the high threshold? IIRC TSM won't start new automig processes when migration is already running, and will only start as many processes as there are different clients having data in your pool. Also, check out your mountlimit on the tape devclass.....
Furthermore, your disk pool might not be fast enough to keep your drives streaming. -- Met vriendelijke groeten, Remco Post r.p...@plcs.nl +31 6 248 21 622