I am getting ready to order a new 2002 Dodge 2500,regular cab 4X4 with a Cummins Diesel. I don't pull a trailer or camper but have owned Diesel engines for 20 years and like the economy and durability if taken care of. My question is this, I had planned on ordering the 3. 55 limited slip gear ratio but don't know if I want the 4 speed automatic or the 5 speed manual. I presently drive a 1990 Dodge Cummins that has the 3 speed automatic with a 3. 07 limited slip gear ratio and get around 18 mpg in my driving. My driving is 70% highway (65 and under), 20% city and 10% pasture. If driven right with a light foot should the 5 speed get better mileage than the 4 speed automatic. I just want some insight from people who have owned and driven the new ones.