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!

JB QLU FVEICLQB CNX BNG RFO WUFX QLIT EB PWIUOX I FE IEDWUTTUX AUWB YUVV XNOU BNGW TNVGQINO MUB IT OWWFWCJJWNJL QLIT VIQQVU RLFVVUOCU YFT ONQ QNN LFWX YFT IQ