first, how many lines do you update?

second, haveing any index that supports "where account_number = c_one; "? if no, create it, if yes, try to rebuild it.

therd, check function "mod(county,1000) " (to me it looks like a function) for preformance problems. see if your probrm is there.

and last, check you cursor, you may find the select statment there to be preforming very bad. check index in your where clouse, rebuld theme if you need.