Originally Posted by Chromeshadow

I have an underdrive pulley in my 2000 3.8, It was about $250 including the belt. I did not need to replace the Harmonic balancer.
The belt is easy to buy at NAPA when it wears out, you'll need to save the PN on the belt or take the old belt in, they can cross the gates number or get a gates belt...I put over 100,000 miles on the belt before replacing it. I elongated the mounting holes in the crank position sprocket, you have to take it off to replace the pulley, I advanced the timing about 3 degrees. I got a noticeable increase in power and about 1.5 miles per gallon improvement. I have 195,000 miles on it, so it paid for itself several times.
You will need an 200 LB or higher Impact Wrench to get the bolts out, and a longer crank bolt to get the pulley back on. Tapping it on with a hammer can mess up the crank bearings. It's a pretty easy DYI mod. It did not effect the battery, the AC does not get real cold at an idle, but was never a problem in LA or AZ.