I am having the same 2 problems with my 98 blazer. The problem with the 4wd shifting has been a nightmare. The 98 blazer has an electrical encoder motor to switch into the different drives,Chevy no longer uses the vacuum switches. My mechanic told me the computer said the motor was bad, But he didn't feel confident with trhat because everyone he talk to said these motors never go bad.I took it to the dealer to have it diagnosed and they said it was the motor. My machanic replaced the motor today and guess what it still doesn't work. If anyone has any ideas i could use some help,i'm already $500 in to this problem with a spare encoder motor since they won't take it back.