Little issue (btw. any super 6 stuff not ur not using?)

A couple of the best "mods" that I've done to help idle quality is switch to the long electrode plugs ( autolite 985 or the NGK ZFRN5? i forget) look up a 2000 jeep cherokee with 4.0L. And the fuel line mod: basically moving the fuel line away from the waterpump/exhaust manifold and running it straight up from the fuel pump and over the valve cover.
I've been tinkering with my super six for a few months now and just recently got it to run normally (intake/exhaust leaks) Check out www.remflex.com for manifold gaskets, a little pricey but never have to worry about it again.

I will agree with mullinax95 on the crazy ammeter, The voltage regulator gets reference voltage from the battery, therefore when the engine slows enough for the voltage to drop, the regulator lets more voltage to the field coil of the alternator and voltage goes up at the battery causing the regulator to now throttle back the field coil = vicious cycle = wildly bouncing ammeter. Also take a look at slantsix.org, huge number of posts to sort through but there is lots of good info.