I run an ampeg b2re through a 4x15 hartke cab and a 1x10 Ampeg cab. I play in a band that does 4 set nights. By the second half of the night (after the unit's been on for 2-3 hours), the volume starts fluctuating. It still outputs to XLR at full volume. It just loses stage volume. I've replaced all power pieces (got a pro 6-prong and extension cord) and all speaker wires. Is this thing overheating? Should I turn it off during the 15 min breaks? Or is it something else? The kid who sold it said no need to change anything ohm, so I have never touched that. Should I? Thanks for your help!