I cured mine with the same problem with 1 gauge cables and a 1000 CA battery. It was fine for about 10 years and now it’s doing it again. It’s a mystery why ponchos are afflicted with this. My motor is getting swapped this winter and I will be replacing everything. Hopefully I won’t have the issue any more. The high compression 428 in my GTO turns over fine. Go figure.

One thing to try is one of the mini high torque starters. They are pricy though. Butler sells a modified one that fits better than other’s