I have 1998 Dodge Durango. It's a 4x4 5.9L v8. I'm looking at replacing the transmission and seeing as I don't really need 4wd in the city, I'd like to get better fuel economy and better acceleration.
The question is whether or not it's cost effective/good idea to turn this pulling machine into more of a muscle car machine by swapping the tranny and rear differential?
If the transmission is slipping now a rebuild will give you a slight gain in mpg. If you have the optional towing differential with a 3.92 ratio then changing to the standard 3.55 will also yield a small gain. This will hurt acceleration though, while increasing highway mileage. The biggest issue is "cost to benefit" ratio and the time to recoup those costs that are strictly to increase mileage. The Durango is a heavy vehicle with a large motor. A realistic mpg would be 12-14 in city driving. If the gear change and tranny swap netted a 20% gain (this would be a huge gain) to 14-17 mpg. With a cost of $4000 (ball park estimate). At 15000 miles per year the fuel savings would be about 350 gallons per year. At $3.00 a gallon that's 4 years to get a return on investment on a 17 year old vehicle
"Better fuel economy and acceleration" are typically mutually exclusive.
You'll gain one at the expense of the other.
The easiest way to influence these is by the use of your right foot. Unless you can significantly improve the power to weight ratio of the vehicle by shedding weight.
Before you go too far you might want to consider the cost of your changes and the anticipated fuel savings. In many cases it will take many years to get a return on your investment.
