hey guy i have a smarttech buggy and it did the same thing.come to find out the smalldrive gear in the rear gear box had worn down.
it did as you described,roll freely then not then roll freely again.it was worn so bad that it wouldnt catch the other gear like it should,
and it would bind then roll freely again.could be in the front or rear of yours if that is the problem.hope this helps you,let me know what you find out.