Never heard of PDQ. You can find a used SCT SF3/X3 for half the price of a new x4 if you are looking to save money. Just have to make sure the previous owner has it unmarried. I have tunes from Tony Wildman, WPE, PHP, and TSD. They all have their pros and cons. Highly recommend PHP and TSD.
Tony Wildman (Total Diesel Performance), WPE (Windrunner Performance Engineering), PHP (Power Hungry Performance), TSD (Truck Source Diesel)