If reprogramming modules and the radio, you need the 24 month subscription.
So you can't adjust the radio volume at all, not even on the unit itself? Does your 2500 have volume buttons on the steering wheel? Have you tried just having the ignition switch to aux power only, not run? At this point, it should operate normally.
Did your truck have Bose? These Nav units were normally installed in trucks with Bose. What year is the Nav unit from? There was a change at some point where they went from non-Lux to Lux or the years just won't work with your truck. The unlock you got probably just eliminates the requirement for the VIN to be programmed into it which should allow it to work in any compatible truck.
If nothing works and it's the right year/model for your truck, I would assume it's a problem with the radio itself. The volume button is a mechanical one and should just work no matter which vehicle it's installed in.
Personally, I wouldn't even bother with these old units. They're no longer supported or updated and are just clunky. Had that experience when the one in my 2010 Avalanche tried to take me down a no longer existing road or didn't know about newer roads.
