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!

FV RTK ZEWPSTRV SIJ VIC QZN GKZJ RTPB WV AGPKNJ P ZW PWXGKBBKJ OKGV LKEE JINK VICG BIECRPIN HKV PB NGGZGSFFGIFT RTPB EPRREK QTZEEKNSK LZB NIR RII TZGJ LZB PR