1998 tahoe 5.7 vortec slow or no start when hot...

My 1998 Tahoe cranks(spins) fast first thing in the morning(cold) and usually cranks on the second turn of the engine. When it is has warmed up it sometimes cranks slowly like the timing is way off or bad starter. I say sometimes when warm because it does spin normally at times and cranks, grinds slowly but cranks, grinds slowly and then stops the starter from even turning with no crank. I have replaced the starter twice, replaced the crankshaft sensor(relearned), battery has been tested multiple times, verified that the distributor is pointing to #1 and cylinder #1 is at top of stroke, have two pcms, have cleaned all grounds that I know of, have run resistance test on negative and positive cables, fuel pressure is fine, and have had a tech II tool say everything when running is in spec. Purrs like a kitten when running. At the moment I am at a loss. Thanks for any help

Corrosion can be hiding under the sheathing of the Batt cables where you wont see it. A resistance test will not show this. So I would suggest you replace both Pos & Neg Batt cables.

The IGN switch could also be an issue. The Crank switch is one of five separate internal switches.

Turn on the headlights when this happens again. If they go dim or out then I would suspect the Batt cables.

Welcome to the Forum and good luck.

Corrosion can be hiding under the sheathing of the Batt cables where you wont see it. A resistance test will not show this. So I would suggest you replace both Pos & Neg Batt cables.
The IGN switch could also be an issue. The Crank switch is one of five separate internal switches.

Turn on the headlights when this happens again. If they go dim or out then I would suspect the Batt cables.

Welcome to the Forum and good luck.

Thanks for your reply but I did a test by removing the spark plugs to see how the engine spun and it did spin fairly well. I then put my compression tester in to just to see what the compression was and the starter almost stopped on the compression stroke of that cylinder. I then removed the starter and took it back to autozone to have it tested. It passed the tests but they gave me a new one. The truck now cranks fine but this is the third starter in a year and only 4 months since the last exchange. I don't know what is causing the starters to go bad. All three have cranked the vehicle fine when just replaced but have seemed to gradually die over a short period of time. I have never had trouble with any other vehicle starter from Autozone so this many seems odd to me. Any thoughts anyone?

I'll bet a dollar to a doughnut you'll be changing it again if you dont replace those cables and renew all connections and grounds. A new starter has lower resistance. The high resistance in the cables creates excessive heat in the starter which in short time will damage the starter solenoid contacts, armature and brushes.