Sand isn't abrasive enough to polish the high-Rockwell steel used in Cummins heads. Usually it's the aluminum-headed BMW's or Audi's that port and polish with just sand.
For your truck, you need an abrasive agent in a liquid slurry. The liquid is to slow down the particles as they move through the intake; we run a lot more boost than other vehicles, and you need to give the stuff time to do the polishing.
The best thing to use is a combination of black powder and kerosene, mixed together until it has the consistency and appearance of chocolate cake dough.
To avoid it from igniting, you want to remove your injectors and valves before putting it into the air intake and cranking. Air filter is a good idea to remove too, but not necessary. The slurry will actually coat the filter like the oil stuff K&N sells, and it'll filter even better.
Your idle is probably messed up because you have sand deposits left in the valve stems. The liquid should clean that up in addition to porting and polishing your head.
PS. Yeah, you seriously could come up with an original "look how stupid I am" thread...