MSD boxes work well when they're working, but they're notoriously unreliable. I carry a spare in the trunk of my car. Whether yours is bad or not, I'd recommend you pick up another to carry with you. I put quality plugs (I used this kit with heavier duty plugs on the power and ground lines -
https://www.amazon.com/Weather-Pack-...=A39ZZJ3OT79TI ) on each lead so that if I have to swap it out it's a 5 minute procedure rather than running new wires each time I need to swap it. It also makes troubleshooting in cases like this easy - I can very easily just swap the MSD box over to the other MSD box to confirm or eliminate the box as the source of any issue I may be having. Not only are the MSD boxes unreliable, but their failure can drive you nuts when trying to diagnose because the failures manifest themselves in many different ways.
I guess that's all a long winded way to say buy another box and swap it in to see if it helps. It won't cost much and I'd highly recommend that you carry a spare anyway so the money will need to be spent either way. It's also not a bad idea to pick up a spare magnetic pickup for the distributor to carry with you, as they're equally prone to failure as well. MSD stuff works really well but their products are sadly not very reliable.