2001 blazer stumbles between 50 to 55 mph no other time plugs are new cap new but it pulls up codes on crank and cam sensors why would they just miss fire at those speeds

 

Intermittent conditions can be caused by faulty wiring, loose components, etc.

But lets start with the specific codes. Your PCM is trying to tell you what's wrong.

 

Question cam sensor can be replaced by rookie but the crank needs to be replaced at shop right? replaced plugs thet were gapped at 75 and the one behind steering shaftwas real black

 

Either may require a CASE relearn (aka. crankshaft variation learn procedure) to properly calibrate the PCM to the variation of the new sensors. Either can physically be replaced in your driveway.