Over the last few months my starter's been cranking more and more slowly, so I upgraded to a newer LT-1 starter a few weeks ago. It worked fine at first, but day-by-day it began to crank slower like the old starter until it just wouldn't crank on me today. I had to wait a few hours before I could try it again and finally turned over fast enough to fire up the motor. So I replaced the battery today, and it hasn't solved the problem.

It really doesn't wanna crank when it's hot, but even cold it's very slow at turning over. It was suggested to me that the starter circuit might have a few weak spots where the connections might be dirty or otherwise and impeding the full 12 volts down to the starter solenoid. I think there might be heat soak at the starter wires based on the above conditions. Any ideas?

So far, the components recently replaced are:

Starter
Battery
Cap & Rotor
Ignition Module

 

do u have headers if so ur starter soleniod my be getting to hot,it happend to me with my slp 1' 3/4 headers so i hooked up a ford starter soleniod to it,problem solved but make sure to check voltage at soleniod when hot and make sure ur timing is not to advanced,will also cuase slow crank when hot

 

Aside from the LT-1 starter, the car is bone stock. They did advance the timing about 3 degrees beyond normal to give it that extra punch, but I wouldn't know if that's enough to cause slow cranking. I guess if there's slack building in the timing chain and the advance is getting further off, I'd get slower cranking. How do I check what the timing's set to?

 

Hook up a timing light.

 

The timing wont affect how fast the engine turns with the starter. It will however make it start harder or slower. But the engine will spin the same speed with the starter.
How old are your battery cables? You could try that. My guess is probably a starter getting to hot.