Karl, I think you need to re-do your grounding. The low voltages is a tell-tale sign.
You can have continuity but still have poor current capacity. In other words, you need to clean off the contact surfaces where the ground strap is bolted as well as the other ground points.
And I'm not sure the intake is the best place to ground. Remember, what the ground strap is really for is the starter and it's bolted to the block. The intake is bolted to the heads so the current has to go through the bolts only since there are gaskets everywhere. Normally, a torqued bolt only holds by the first 1.5 thread turns. With a little grease or thread lock, the conductance can be severely diminished.
If I were you, I'd go over all the grounding surfaces and clean off the paint and apply some copper paste. If you still want the ground strap to connect to the intake, I'm afraid the paint will have to come off.
Also, I don't really see the point in having two connections to chassis. The 10Ga is either redundant OR it is the best connection to ground in which case it is insufficient which will cause low voltages everywhere, especially when cranking.
