Originally Posted by maliciousteve
I get this feeling for sure. It's the dryness of the Mark series amps. I have a JP2C which is phenomenal, but every once in awhile I find it uninspiring so I play other amps. When I come back to the amp after a month or two, it sounds amazing and I wonder what the heck I was ever thinking. They're just SUPER dry sounding amps. But man do they sound great cranked up and great recorded.
I would honestly say the amp the Lamb of God used for a decade is aggressive enough, and I believe it was the amp Hetfield used on AJFA in 1988, which was arguably Metallica's best guitar tone to date. You might want to mess with your settings, tubes, and overdrives you put in front of it to see what else you can get out of it. I've gone through a ton of overdrives myself and kept the 1 or 2 that really fit my amps the best.
Having said all that, if you keep the Mark IV, and you want another amp, I would suggest one based on the SLO circuit. So from low to high $$$ - Peavey 5150, Mesa Dual Rectifier, Soldano SLO 100 (They have a 30 out now too). I suggest that because it's a whole different approach to gain than your amp, though it's complimentary. You'll feel good going back and forth between them, which is why a lot of guys have a 5150 and a Mark amp, or a Dual Rec and a Mark amp, because they're two very distinct feels.
Just my $.02. Plus there are less and less Mark IVs in the marketplace right now, and if you let yours go there is no guarantee you could get one back. It's one of the best amps Mesa has ever made. I'd rather they included Simul-class on the JP2C instead of the throw-away Cab Clone, because that big clear bottom-end you get from a Mark IV or a 2:90 is just spectacular.