Ted65000

I have a 1995 K1500, 5.7L, with 180,000 miles, and I am not the original owner. The truck will not shift out of park. It has been difficult to shift at times, but the problem was never consistent until now.
This is what I have tried so far. I assumed it was the brake to shift solenoid or that the brake light switch was bad. The brake lights work. So I looked at the brake to shift solenoid, and found that someone previously disconnected the wiring. So that should not be the problem.
Using a screw driver, I pried the brake to shift solenoid arm off of the column shift mechanism to insure that it was not a mechanical failure in the solenoid jamming it. I was still unable to shift out of park.
Looking under the truck, the shift cable is in good condition and looks to have been replaced at some point in the past few years. I pried the shift cable loose from the column shift mechanism and can pull and push the cable to shift gears. With the cover off the steering column, I can see grease leaking from the shift mechanism.
So I am assuming that all I need to do is replaced the column shift mechanism. It appears to be held in place with three socket head screws. Has anyone replaced this before and is there anything I should know before I start? It looks easy, but I was wonder if there was anything critical I should know. I am assuming I should use some blue lock tight as well? Does anyone know what the small cable that runs to the key is for?

Update. I ordered a replacement shift mechanism from an online supplier, which was around $90. To remove the old unit I disconnected the small cable that ran to the starter switch. There is a slot for a small screw driver to fit in to release the cable. The cable has a plunger on the end of it and when you turn the key, it unlocks the shifter. I should have checked that before ordering parts as the problem could have been with the key mechanism not pushing in the plunger. The shifter handle comes off by removing one screw and using something to beat the part loose. There was a lot of corrosion holding it in place. I had previously used a screw driver to disconnect the shifter cable and the brake to shift solenoid arm. Next was removing the three T27 socket head screws and the old shifter was off. These three screws had some sort of thread lock on them still visible. I used blue Locktite when putting them back in. Retightening the screws did not feel very good; it felt like I could possibly strip the threads if I was not careful. Maybe I should have cleaned the threads before reinstalling them. I could not get the shift handle all the way back into the shifter and could not reinstall the screw. It is probably the corrosion causing the problem, I though a little oil would help, but it did not. The handle is currently jammed in place, I will have to remove it this weekend and try cleaning the corrosion off.