I have been having charging trouble with my underdrive pulleys. At night, everything would dim at idle. I just installed a 1 7/8" overdrive pulley from ASP. It's charging fully at 700rpm idle now. I went with the 89.5" belt and it's perfect size w/AC.
I've been running an overdrive alternator pulley on my car and truck for a while now and it works great, I had to turn down the OD of my socket on a lathe at work to install it though
Running a 130 amp alternator is not the "fix-all" for under charging at idle. You can have a 130 amp alternator and still spin it too slow as to cause charging problem.
At the same time, it's not necessary to upgrade to an alternator capable of 130 amps if you don't have enough electrical gizmos and doo-dads that require it.
Does it hurt to go to a 130? Not at all, but it's not always necessary either.