Not sure how much fuel your rig will hold. I would put no less than 30 gallons on and then get yourself a bottle of PowerService Diesel Kleen, grey bottle. Add according to the directions on the bottle. And then go for a drive of no less than 100 miles. It would be good to have a good long stretch of interstate in there and some hills if possible so you can exercise the machine. Things likes seals can dry up and other things when not heated properly can deteriorate. If you are running the engine periodically it needs to be run long enough to come up all the way to normal operating temperature for at least 5 minutes. In a diesel this can mean 20+ minutes at idle.