OK, Now it DOES sound to me like a weak battery. They can turn the starter slowly at first, seem to stop at slightly BTDC, then then move it a bit faster as the piston moves past Dead Center, when the ignited mixture helps push the piston. From this point, if the fuel is igniting, it will eventually start.
I suggested this approach in another thread just recently. If you have a multimeter, leave your hood up when you park the truck at night (if you can). Then, in the morning, check the voltage at the battery terminals - without opening any doors or doing anything that would put a "draw" on the battery. If it's below 12.4 V, I'd almost guarantee the battery's bad. Anywhere between 12.4 and 12.7 V is "suspect" (get a load test) and at or above 12.7 V is good.
- Jack
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