Has anybody used Slick 50 in their Cummins? What about the Slick 50 auto trans additive (for older transmissions)? My tranny is doing okay, just thought if this stuff would help, I'd try it.

 

Slick50 has teflon solids that DO NOT (IMO ) belong in any IC engine or trans. In fact the makers of slick50 were sued by the FTC for false claims of the product, see here
http://neptune.spacebears.com/cars/legal/s50fcn.html

I would just run a good diesel rated oil in the engine, and for the trans, I use lubegard in the red bottle
http://www.lubegard.com/automotive/trans_atf.html.
just my .02

 

I'm with Chris on the Slick 50 (as well as most other additives). As a whole, they tend to be a waste of money and some can even be harmful.