Even with no key in ignition and emergency flasher off. Truck had problem with hard starting in the first place. Had a few guys came to help....
I had a similar problem one time. Truck shut down going over a bump or climbing a bridge. Finally found problem with main fuses for the red power...
I would check your throttle valve. The valve is right before the intake manifold. I've replaced plenty of those valves recently. Also check oil...
Check your alternator overcharging. I had same problem last year that you have but loss of power in 7th gear and up
