checking voltage during travel is dangerous and not worth much in this sort of diagnosis. lifting takes far more current than drive and during drive there are other currents that happen at the speed of light (so your meter could not show them) that affect the reading you will show on your meter.
all that said, the flashing 10 on the vehicle manager is a far more important indicator of your problems.
1st, have you checked all the fuses on this truck, either by removal and ohms or by voltage drop on each side of the fuse?
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