It doesn't sound like you have vacuum to the 4 wd or the HVAC system.

 

I pulled the vacuum line going to the Tcase switch and I figured it was supposed to always have vacuum in one of the 3 ports but I didn't feel any at all

 

The first place I look for vacuum is at the reservoir. Disconnect the line at the fender and listen. If you hear air, it was holding.

 

If there is some but not much vacuum the HVAC vacuum, say due to a leak in a hose or a hose loose on a nipple fitting, the actuators will sometimes work depending on the manifold pressure; i.e. more likely to work properly when at idle or cruise (more vacuum) and less likely when under hard acceleration (less vacuum). The vacuum reservoir is designed to compensate for those situations but if there is a cracked vacuum line, then the system will leak down eventually.

If there is no vacuum at all to the HVAC system, then there is either a plugged system, a disconnected hose, or a bad vacuum leak which could also affect engine performance. Also even if there is no vacuum, the actuators will default to their no-vacuum positions. This I've heard will be to the defrost setting as that would be the safest fail-safe configuration.

After looking at the Posi-Lok product, I would guarantee that it would be much easier and less expensive to try to fix the vacuum lines. Unlike with the Posi-Lok system for which you would have to get underneath your truck, all of the vacuum line repairs are done from the top of the engine compartment with the only items that would have to be removed being the air inlet to the throttle body (to get at the vacuum supply hose on the intake) and the battery and battery tray (to get at the actuator for the front axle).

 

One advantage of a cable lock set up is you can leave the front not engaged and have 2low only to the rear tires

 

I use 4 low for pulling things that I know are too heavy for my 2 door and I understand that 2 low steers without binding but every time I've needed the low range for added torque I've also needed the added traction of 4 wheel drive. I can't think of a practical reason for 2 wheel drive low range. What would you use it for?

 

Having 2-Lo would be like what was in my father's old 1966 2wd Chevy 3/4 ton pickup in the form of the first gear being a "granny gear." If I had 4-Lo I'd be hard pressed to think of a time when 2-Lo would do a better job except maybe towing a very large load on a road for a short distance.