"... maybe i should change to p89c61x2 and get another 10 bit a/d converter ..."

Since you appear to be willing to add another device, you could also consider staying with the '552 and adding an external UART. For example, the MAX3100 (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1731 can sometimes be "thrown in" in a pinch when you need an extra UART, since it uses SPI (only 3 wires). Have the '552 handle either transmit or receive, and the MAX3100 handle the other direction.