I just picked up a 01 Silverado 1500 for some light plowing. It's a 4.8L with a NV3500. When I test drove it, all was great. I put it in 4wd and reversed quickly and 4wd was working. It just gripped and i could see in the dirt that all four tires were engaged. So I brought it home and installed my plow. I was out back getting some railroad ties for weight in the rear when I went to put it in 4wd and it wouldn't engage. The 4WD light on the upper left side of the dash comes on... not sure what that means. I did some little tests to try to narrow it down, but it was getting dark so I could't do much more. First I parked it on flat ground and when in neutral and 4HI, I tried turning the front driveshaft by hand. It only spins a tiny amount due to slop in the chain... it seemed like a normal amount. I could see the rear driveshaft moving too, so the transfer case seems to be working alright. In neutral and 2WD, the front driveshaft spins freely. So now i figure the only thing it could be is the hubs not engaging. So i removed the actuator from the axle housing. I plugged it into the wire harness and left it dangling. I turned the key on and put it in 4WD and the actuator shaft came out a little more than an inch. I took a long screw driver and put it in where the actuator goes and pushed whatever is in there in. At the same time, I spun the front driveshaft by hand and could see/feel the front half shafts trying to move. So it seems like everything inside the front axle is also good. The only thing i could think of is that the actuator is on its way out and doesn't have the strength to push the hub locking mechanism. I do have a 2002 Silverado 1500 that i think i'm going to pull the actuator off and see if it fixes it. Is there anything else I should try??