I'm pretty sure it's with receiving the data because I have a counter that expects a 256-byte packet every second or so. I will see all the right data, but certain bytes will drop out. For example, if I send this data (showing 16 lines of 16 bytes):
################
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
################
I will instead see:
################
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#--------------#
#-------------##
--------------##
--------------##
-------------##-
-------------##-
------------####
############
(only 252 bytes received)
Notice that occasionally bytes will get dropped. At 57600 baud, I don't see this problem.