Dodge Caravan Brakes sticking

My 99 caravan has a problem where the Brakes get "stuck". It happens
intermittentely...
I recently replaced both calipers, (I assumed they were frozen) because
of this problem. Now, it still happens...On one occasion, my wife came
out from shopping and noticed that the brake lights were lit (as if
someone was stepping on the brake peddle). Could this be a master
cylinder problem?

We rarely use the emergency brake, but I admit I havn't looked at the
rear brakes yet.

Thanks in advance for any help!