PIC18F4550 to 18F4553 Comm Issue?

[Demon]

I see no reason why you couldn't use an external 20 MHz crystal on the 4550 and 4553, and run them at 48 MHz.

Try with these settings, I know these worked.

' 184550 external oscillator 20MHz
...
DEFINE OSC 48
...
DEFINE HSER_RCSTA 90h               ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h               ' Enable transmit, BRGH = 0
DEFINE HSER_CLROERR 1               ' Clear overflow automatically
DEFINE HSER_SPBRG 25                ' 115200 Baud @ 48MHz, 0,16%
SPBRGH = 0
BAUDCON.3 = 1                       ' Enable 16 bit baudrate generator

I used 22pF ceramic caps on the crystal.

Like these round brown ones:
http://www.capacitorguide.com/ceramic-capacitor/

Also, notice this has a low error percentage despite the higher rate, only 0.16% compared to your 1.36% (I'm assuming negative is irrelevant on this value, I could be wrong).

One last thing, 48 MHz on the 4550 would let you use USB later if that's a requirement.

Robert