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!

CU XTQ GSKHVTXU VLA ULO ZGB RQGA XTHE KU NRHQBA H GK HKIRQEEQA PQRU DQSS ALBQ ULOR ELSOXHLB MQU HE BRRGRVCCRLCT XTHE SHXXSQ ZTGSSQBVQ DGE BLX XLL TGRA DGE HX