[gtofreek]

Get the ground cable off the exhaust. The factory did it there, but that is a very poor place to do it as the connection will get worse over time. Maybe relocate to a hole in the front of the head, or one of the bolt bosses right under the valve cover rail. A good GM starter should have no issues what so ever turning over your engine.

Take a volt meter and when it is cranking slow, connect the neg lead of the voltmeter to the negative battery post, and the positive lead to the other end of the negative battery cable where it bolts to the block. Crank engine over and read the voltmeter. There should be no reading if the cable and connection are good. If it reads .3 volts or more, you have a ground issue. The higher the reading, the worse the connection. If you get a reading of 1 volt or more, that will cause a serious starting issue.