Things to test.
Get rear tires off the ground with jack stands. Put tranny in neutral and depress clutch pedal. Start engine. If rear wheels spin forcefully, then the input shaft pilot tip is binding in the pilot bushing.
Shut engine off. With tranny in neutral, and clutch pedal depressed, ask someone to try to turn the rear wheels by hand (truck still on jack stands). If turning is nearly impossible, or you feel the engine crank/pistons moving - again confirms the pilot tip is binding.
