Q: Starter circuit problem and will not crank. 2000 GMC Savana 2500

My van is having a starter circuit problem. While I was filling the tank at a gas station, my van would not start. I had to push it away from the pumps and it then started. When I got home and turned it off, it would not restart. I have checked the battery and failed load test and replaced, but no change. I then followed the circuit to PnP switch but no signal through in park; bypassed to verify and replaced the switch. I found a bad starter relay and replaced it. Still no change. Then, I checked the starter signal and I do now have a signal but the van still will not crank. I removed the starter. Except for worn brushes, the starter was fine but I went ahead and replaced it. It will now kick the starter, but still will not crank. I have checked all fuse block power and all is fine there. The battery has full power and it also passes a load test and a visual inspection of the wiring. There are no breaks and no corrosion. In the starting circuit, all components checked out okay. I tried a test jump at the starter to bypass any other possible problems, but the van still will not crank over. The starter engaging can be heard, but it will not crank. It did start twice, but not cranking over. I also inspected the ground from the battery to the the engine block and braided strap to frame. Except for some road dust, it seems dry and no sign of corrosion. Without my van I am losing income, so could you please tell me what you think I need to do next to fix my vehicle. Thanks.