1998 Chevy Blazer ready to shoot it computer problems

My chev blazer I bought used two years ago. The AB brake light and air bag light other come on and off. We put in a new fuel pump 6 months later put in another fuel pump. Now we need a new transfer case for the 4 wheel drive. With a truck this old is it worth purchasing a new transfer case or used with 20 to 40 thous miles on it? Also would the O2 senser act with the computer to tell the truck there is something wrong that may not be? With the AB brake light allways being on our anti lock brakes will lock up on me on a summer day with no snow. When we put in the fuel pump we disconected the comp. All lights were off for a week or two. I have put a lot of money and work in theis truck it looks brand new sharp truck but the work and $ are killing me. Do I shoot it or not?