Upload chokes between 30,000 and 40,000 rows

Great plugin. I’ve been able to use this up to a certain point. I started testing with small amounts of data, but our user base contains more than 175,000 usernames. That choked and never recovered. I started testing with files of 10,000 and incremented by 10,000 until the plugin wouldn’t work. I have it choking somewhere around 30,000 to 40,000 rows in the CSV.

Any recommendations on this?