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!

DV OMT PAWGXMOV XFE VFS NPQ JTPE OMGC WV HJGTQE G PW GWZJTCCTE YTJV BTAA EFQT VFSJ CFASOGFQ LTV GC QJJPJXDDJFDM OMGC AGOOAT NMPAATQXT BPC QFO OFF MPJE BPC GO