1995 Cadillac Concours V8 Front Wheel Drive Automatic 108000 miles

I have replaced battery,alternator,fuel filter,checked starter. after driving for awhile it just stops.It starts right away in park not in neutral.put topside mount battery on it to see if it would help with connections.If you idle to long once you start going it stops, everything just shuts down.I live on a dirt road and have been told that the acid in the battery could travel back through the cables, that is when we cut the original cable end off and direct mounted the ends with clamps. I hope you can help as I am disabled and terrified of it not starting one day.I just filed bankcrupcy and do not have a credit card if you could help I would greatly appreciate your time.
sincerely, joeysnana2@gmail.com P.S. It drives ok on a 2 hour trip. continuous driving