After I drive the car and turn it off let is sit for a couple minutes and try to start again the starter will barely turn the engine over. Heat soak? It is an after market high torque starter. 350 with headers. Heat wrap instead of heat shield.

 

Maybe your battery cables and connections are corroded or dirty.

- Eric

 

I had exactly the same problem with my 1970 98. I had to shell out $25 to get a jump when I went to JoAnn's Fabrics for my wife and it wouldn't start when I came out (and I had to turn in my man-card for being observed shopping at JoAnn's). I replaced the cables, a 3-year-old battery, made sure the timing was right, and installed a heat blanket - no joy. The starter had been replaced 8000 miles/30 years ago, and it was a rebuilt Delco, so I just didn't think it could be the starter. I finally decided to get a new rebuilt Delco from Napa, installed it and the car now starts well no matter how hot it gets and is fun to drive again. Maybe the experienced mechanics here can explain why a starter w/8000 miles on it quit working when the engine was hot. Maybe whoever rebuilt it didn't do a good job, or maybe since the car was rarely driven and sat in a garage some of the inside parts of the starter corroded.

 

The GM starter hot start problem is caused by two things. First is pitted contacts in the solenoid, and second is excessive voltage drop in the starter circuit. The common misconception is that the Ford solenoid fixes this problem. Actually, it doesn't, as you still need the contacts in the solenoid to work for the starter to turn over. Be sure your solenoid contacts are in good shape. If you are concerned about voltage drop, look at this thread, especially posts #12 and 13.

And keep in mind that starter wrap will also keep heat IN the starter. No insulation is perfect, so depending on how long you drive the car, the starter will still heat up. Insulation means that it will take a lot longer to cool down.

 

For slow crank when hot symptoms, I would first check battery condition and state of charge. Then check battery cables for corrosion and connection integrity at the ends of both cables. If this is all good the next step would be to remove the starter and have a look inside for problems or replace it.