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 TKV UCYOSKTB SHG BHN DUI LVUG TKOZ YB PLOVIG O UY OYALVZZVG FVLB XVCC GHIV BHNL ZHCNTOHI EVB OZ CPLOIHDIUSCO TKOZ COTTCV DKUCCVISV XUZ IHT THH KULG XUZ OT