You're not going to notice much of a difference in gas milage with a 4.36. Me and Epstein used pretty much the same amount of gas on a trip to deals gap last year. He had a 4.36 + helical I had a stock 4.08 + helical and I'd always ask how much gas he used and it was with in 1/2 gallon of my car each time. That was about 1500-1700 miles of driving.