I'd replace the ground straps with something a little bigger, at least 4 gauge wire but I prefer 1/0.
And check the hot wires between the battery, starter, and alternator.
I recommend doing the big 3 under the hood on these trucks, the stock wiring they used just isn't very big.
you can check out how I did it in my build thread.
http://67-72chevytrucks.com/vboard/s...d.php?t=375526
I added an additional ground wire between the block and battery (making it a "big 4" i guess lol) and plan on replacing the hot wire to my starter soon, the stock wire has a low strand count and it's stiff and hard to work with.
I didn't check my idle voltage before I did it, but after it's 14.5-14.6