SFK spoke volumes for me. I have it back on the shelf and went back to my GDE tune. Wish I never wasted my money on SFK. Much happier with the GDE tune and I feel my truck will last much longer. Runs cleaner, less regens and better fuel economy. Jimmy never gives answers and seems clueless as to what he is really doing. He is very evasive and gets angry easily. GDE truly understands these trucks and can therefore offer real knowledge.