I read your post as far as the second truck goes you said it sometimes backfires and runs bad and you looked at the cap and wires and plugs rotor with out a lab scope to trace it down l would replace the distributor you might have a bad coil in the distributor replace the complete unit. As for the first truck l know you said you checked all wiring with another truck and you had the dealer in to look at it. It sounds as you are loosing power to the motor recheck the e-thro fuse 15amp in the fuse box make sure with key on you have power that fuse goes to the ecu to power the motor