Peavey TNT 150...time to upgrade???

Hey guys, Ive been playing small clubs with my TNT 150 for a while now, and it has been a work horse, however at our last gig I ran into something that has never happened before, my sound just cut out intermittently during the last 2 songs of our set. Any ideas as to what caused this? I was turned up louder than normal, I normally play with the volume on 5 or 6, and this night I was sitting at about 8.5.....was it a little too much for the amp?

I have been thinking of upgrading my rig for a while since we will be playing larger venues next year, but I want something that is going to be as reliable as my old stand by. I'm on a small to medium budget.

Any suggestion on a good RELIABLE amp head between $300-$450, I'm wanting something with at least 350 watts.

I've seen the Berihnger ultrabass4500, but I'm REALLY leery of those since you can pick them up at pawn shops for $150 all day long.

I would like to know what you guys are using and what you would recommend.

Thanks,
Infernus Mc Burnus