Update locking systables

Hi Guys.. Im still fighting against Update Statistics routines in DSA 7.30. The medium update locks systables while it's working , and depending on the value you set to lock mode wait to X on a batch process, it times out...i cant use dirty read to because i need a trustful data. We run update during the day and the problem does not happen... But the major problem is Update High, wich whenever i run, locks some large tables that control the authorization of critical procedures (i work in a health insurance company). I dont know exactly if it locks systables, my tables or both.. The question is : i'd rather let update running on a dirty read basis than my Authorization System, but how can i do that? Does anyone else have such problems? Thanks in advance, Gustavo.