I have a '98 P3500... with the 6.5L V8 non turbo. It's been running great but the past two days a couple of minutes after the truck starts up it sounds like the starter kicks on by itself. turning the key to the off position you hear the engine cut out but the starter is still turning the engine. When I moved the key back to the on position(not start position) the engine started up again. This stops after about 10 seconds. Any ideas on what it could be? maybe starter solenoid? don't think it'd be the ignition switch. It doesn't do this every time but has done it twice in the past 2 days and am afraid of this happening while driving the truck. Any help would be appreciated.. Thanks

I would pull the starter and test it yourself.
All you need to do is supply power and ground from the battery with jumper cables. Don't connect the small wire to turn on the relay, see if it will spin on its own, then jump power to the relay and see if it stops when you take away the jumper.

Fix it before it destroys the flywheel, torque converter,
or breaks casting in starter thread area,

BAD things happen, been there done that...

Thanks..got a new starter..alls good now