I have a 1978 Chevy K-10 with a np203 transfer case. It always sticks in 4-Hi. If I try to put it in any other gear, it either doesn't engage or pops out as soon as I move. I am guessing the t-case needs to be pulled apart, and possibly rebuilt. Does it just need to be rebuilt, or is it worse? If it needs to be rebuilt, how much does this job usually run? Thanks in advance.