am I supposed to be driving to engage the 4x4 hi on my 1994 Chevrolet s10 blazer

It should engage either way. You might have a vacuum line that's come off in between the actuator switch and the diaphragm or the switch may be bad also. There's also a ground that runs through the neutral safety switch that will wiggle loose causing the switch to run a code as being bad. Hope this helps ya.