for computing the baud rate for PIC18F4550, the following equation is used:
Baud = F_OSC/(4 * (SSPADD + 1)) ---------- eq.1
according to the data sheet:
SSPADD = 10 for 400k Baud at 20Mhz Fosc.
But by substituting the parameters into equation (1), the SSPADD will equal 11.5
so how is SSPADD = 10?
Give this utility a shot. I came across it across it on microchip's forums while trying to get my dsPIC33f's uart working and it made my life much easier.
http://www.micromagicsystems.com/#/pic-baud/4523812801
Hopefully it will work with the particular chip you are using (it looks like it supports *16, *17, *18 and *24 PICs, in addition to the dsPICs).