I race my 4th gen Ram. I found it better to run with Tow/Haul on. I may be mistaken but it utilizes the 2nd prime before 3rd gear. My truck, with the 3.92 gears, shifts from 2nd to 2nd prime at about the 1000' mark and still pulls hard. When it shifts from 2nd to 3rd it falls on it's face. Our trucks have 6 forward gears but do not use the 6th gear(2nd Prime) unless it is in Tow/Haul or Manual shift mode. I wouldn't shift manually unless you have a tuner that will allow you to change the shift points to a higher RPM. Tow/Haul On = 1, 2, 2prime, 3, 4 Tow/Haul off = 1, 2, 3, 4, 5. You only need the first 3 gears for a 1/4 mile run. If I am mistaken someone please correct me. Thanks.
This is the exact response I was looking for when I posted this thread, thanks.