Along in the same vein, I had a new '99 Ranger 4x4 with 3.0L and 5 speed. It got crap fuel economy with the stock 3.55 gears and had very little power, so we swapped in 4.10 and the correct VSS. That caused it to go from 18mpg to 21 on the highway and from 12 to 15 mpg in town.