i had a 96 cummins dodge 2500. thing would just kinda crank slow. charged the batteries-same problem. tried a new starter-same problem. turns out one of the batteries was bad-wouldn't pass a load test but held a charge fine-huh?! anyway-it took 2 new batteries, and it fired right up. i seems the 6bt takes 2 good batteries to crank it fast enough to make it fire. afterwards, in conversation, i've had 2 other people confirm the same problem and solution.