So i recently purchased a Peavy ValveKing Halfstack tube amp and I'm having some troubles. Everything sounds perfect if i have the volume at about 2 or below but when i turn it up any higher my notes seem to get jumbled and run together. The lows sound OK but my Highs just get lost in the mix. Most of the time this makes it seem like just noise coming out of my amp.

The guitar I'm using is an Epiphone G-400 with an EMG 81 at the bridge and an EMG 85 in the neck . I run it through a line 6 POD XT Live pedle but, I'm investing in a Metal Muff pedal for my distortion.

Can someone please help me to fix this mess??
i would much appreciate it