Walter, I would first make sure that all your fluids are at proper level. Also, have the Towncar placed on an analyzer, ie. Autozone etc, that does it for free and see what codes come up, if any. I also suggest to stay away from transmission flushes, since I find they make things worse. The cause ''' could be ''' burnt O/D bands. You may consider a Tranny shop for some diagnostics...Hope this helps, good luck.