I've replaced both hub actuators now, when I replaced the RH actuator the first try didn't work - I tested the new actuator with a hand vacuum pump and the actuator was bad, but at the same time I was getting weak vacuum from the vacuum line when I ran the engine. I replaced the vacuum hub and it seemed to work okay. But I tried 4WD high and it was clunking a bit, so I'm assuming I still need to work out the weak vacuum issue.

I'm thinking my issue is either dirt clogging the line or a crack leaking air, so either way I need to pull the line off at the least and possibly make a salvage yard run and replace it. Anyone got any recommendations or guidance?

 

It seems like every part of this system is prone to failure. And aftermarket parts are too often non-functional.

Assuming you are talking about a decade old truck, age is almost certainly playing a factor for everyone at this point.