Dang, that's a tough one since we're all burnt out by different things.
I hate to say it, but If you're burning out on one comic, splitting your attention on to two is probably going to hurt (maybe a lot). I tried my hand at having two comics going simultaneously and despite having a large buffer on the original commit, the second one just felt like a chore (in spite of the joy I originally had around the idea).
But maybe a second comic will be more of a refreshing side-project- and if it's exactly what you need to stay motivated and rejuvenated then it's worth a try.
For my personal anti-burn-out methods-
1) Deeply love the work you're making (you know, we all have our own personal art critiques, but enjoying the process really helps even if you're trying to do better).
2) When you're not enjoying the process, take breaks (physical activity/music/an instrument can all be ways of letting your body/mind/soul reset).
3) Take time out to appreciate others' work and feed your inspiration hole
4) Take time to appreciate others' struggles (and help when possible) and feed your community hole. Cheerleading can be so refreshing.
5) Deeply analyze how you spend your time and see what you can cut in order to maximize productivity (but don't forget about the first four points).
Everyone's different so just take care of yourself.
Also, that's outstanding that you've found so much success. Enjoy this moment at the very least.