When you run what happens first, do your legs give out/tighten to the point you cannot continue without straining a muscle, does your stomach knot and turn, cramping up on you, or do you find yourself winded and gassed?
When I run I find that my legs tighten and my stomach cramps well before my lungs give out.
If you can roll for a solid hour, it is quite likely that your cardio is NOT the problem, but rather you have issues with your legs/stomach. The one thing I've done to eliminate the stomach cramps is that I don't drink much water before I run, I just have some energy gel or an energy/granola bar 10-20 minutes before I run, wash it down with a small sip of water, wait for things to settle a bit, then run.
It's different cardio and different exercise.
I trained for a year for a half marathon before returning to BJJ. My running cardio was great. I mean, I ran 13 miles. I could barely roll for 3 minutes straight without being ill.
Now, I can roll for an hour and do 8 to 10, 5 minute rounds and I can't run more than a few miles.
It's defianlty my legs and stomach more than anything. I guess that it is just a differant kind exercise, but I will try not drinking so much water before had as I genneraly do.
Just keep getting on that treadmill, it takes a different kind of endurance from BJJ but running is one of the most rewarding physical activities in terms of making quick gains in your performance. I started running on a treadmill earlier this year and within the first two weeks I dropped like three minutes off my 5k time!
The flip side of that is that if you don't run for like two weeks, you lose it again.
I'd always figured wind sprints were more relevant to grappling