No power

I have a 87 jeep wrangler with a 4.2 L six cylinder. I am having a problem with it just dieing while I am drivng. It will be running great and then it just dies. When I try to start it again it acts like the battery is dead, but I just replaced the battery. After it sits for awhile it will usally start again but then it will die again after a few minutes.

I could really use some help on this!

Thanks,

Bink

so is the starter having trouble turning the engine over, like it's going slow, or just making a clicking sound. Or does the engine just not fire up?