2004.5 Dodge Diesel Issues

[mopower]

I'm new to this forum, so I'm hoping there is someone out there that can help me out. My grandpa put a powerpuck on his 2004.5 Dodge Diesel 3500 automatic less than a year ago (about 7 months I think). He has been happy with it, easy to use, and his mileage went up. He recently made a trip to Oklahoma (set on 90hp) and noticed his mileage dropped from 22 to 16-17. He stopped and fueled up, and when he left the station, it blew a bunch of white smoke out. He eventually turned it off and struggled to get back to 18mpg and never got it. He tried turning the switch to the 60hp setting and he said the truck started missing. He has since disconnected the puck. I haven't actually seen the truck yet, but was hoping for a place to start when I go look at it. Any Ideas??
Thanks !!!!!!

[mikel]

Fill out an rma request and send the tool in to be checked out please.