[squid-users] Authentication retry

I'm managing an instalation with squid and 7,000 users with authentication by
pam_auth.
Frequently, when the load is from medium to high, my browser (and of all
users) doesn't authenticate in the first tentative, tipically accepting user
and password two or three trials later.
It's running in a Sun machine (SunFire V480) with 4GB of memory.

Any idea of what's going on ?

Thanks in advance.

-- 
Gustavo Dagostin da Silva
Divisão de Suporte
Diretoria de Informática
Tribunal de Justiça de Santa Catarina