I have owned a 2012 Ram Laramie 4x4 Dually since new and it's been a great truck. Just purchased a 2021 Laramie 4x4 Dually and will pick it up on sunday. This new one has the HO motor, Aisin Tranny and 410 rear. Have never had a diesel that takes the DEF so this will be a different experience for me. Where is the best place to buy DEF and which brand for this truck. Any input would be appreciated on this truck from you all.