[unruhjonny]

Now, I am not old enough to recall these cars as new, or late model cars, but I had a crash course in this in the mid through late 1990's when I started driving mine daily.

After looking to ensure everything is well grounded, you should look at your starter;
The common rebuilt starters do not use the better core starter - there are visual cues that the one you're looking at is a better one, or a run of the mill one.

With the RA manifolds, there is virtually no clearance for heat shields, so that leaves you to needing a high heat solenoid.

From my experience, the run of the mill starters will have a reduced diameter on the front, and the copper lead will pop through the case right at, or closer to the solenoid;
The better ones have the full diameter of the starter carried right up to the front, and the copper lead for the solenoid will pop out near the very front of the case - and need an adapter to extend the connection to the solenoid.

There are legitimate high heat solenoids both with GM part numbers and 'Standard' brand numbers, but I don't have any of those handy.

Now, going away from original or OE replacement stuff, I have heard that the high torque mini starters work fantastic, as their smaller mass effectively helps them stay cooler.

I hope this helps.