taxsim doesn't have any file size limit, but the cgi interface does seem to restrict uploads to small files. 2,000 records is probably ok. If the file is too large you'll get a "conversion error" and/or a complaint about a short record. In that case please switch to the ftp or ssh protocols. They are much faster anyway and only one or two commands.
I suggest ssh - it can do about 1 million records per minute on a fast connection. the ftp interface runs about 100 thousand records per minute. You can also run on your local machine from Stata or with the low level interface