I used it in my 1500, and sold it that way. I have not yet installed in the 1800. Expect to be getting the ECM done soon, and they'll mess with the coolant then, so will probably wait until next winter to do it.
Great product! Seemed to do a better job of cooling the 1500. I seem to recall that the temp gauge ran a little cooler after installing NPG. Also, the fact that it's supposed to do away with the corrosive effects of water is a real plus.