1992 GMC Truck 4 wheel drive not working

I have a 92' GMC 1/2-ton, 4-wheel drive with 180000 miles on her.

My 4-wheel drive went out a few years ago and I am now just looking into getting it repaired, when it went out it just stopped working, no noisy sounds or anything to tell me that I had a serious problem. The indicator light on the shifter went out and that was the end of the 4-wheel.

I just recently checked the actuator and it was not working, we replaced the actuator and still nothing.

One question I have is what could it be and what will it take to fix it. (When I purchased the pickup the previous owner turned up the torsion bars, the CV axles at the main axle now have a 1/2" to 1" space between the main axle and the flanges on the CV axles).

My main question. Some folks are telling me to swap my axle out and put in a soild front axle? What would this take and what would be the costs?

Thank you for your help.

BO