Oh dear, I guess you have cracked the two caesar cryptos...
This one is more difficult. Although a simple substitution is easily cracked...
Again the characters are limited to A-Z... But I think I can come up with a 256 version again.

Enjoy!

RX FNK ZJEQINFX IAW XAS GZV UKZW FNQH EX DUQKVW Q ZE QEBUKHHKW CKUX TKJJ WAVK XASU HAJSFQAV PKX QH KJIADHUWVEGW FNQH JQFFJK GNZJJKVIK TZH VAF FAA NZUW TZH QF