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!

XP UGT SMCQJGUP JEN PEY ZSO VTSN UGQK CP AVQTON Q SC QCDVTKKTN FTVP ITMM NEOT PEYV KEMYUQEO BTP QK QGMTVVQTKANT UGQK MQUUMT ZGSMMTOJT ISK OEU UEE GSVN ISK QU