Hey I have a 87 s10 blazer that will not go back into 2wd. has anyone else had this problem?

Check the vaccume lines! Very common!

what size motor do you have? if you have the 4.3 there is a vacum diapram under the battery tray that is not letting it kick out of 4 wheel drive. the problem isn't that it is a 7.00$ part. if you look under the blazer on the drivers side there is a vacum port with three hoses going to it. it will be on the transfer case. if you unhook it and take the lines off and take a socket and pull that part out. that part is what is causeing you no to go back to 2 wheels drive.

I had the same problem with my 84 K5. I just went into reverse for about 20 feet, after I switched it and it works just fine, Im hoping it was a one time only problem