Sounds like it could be any component of the starter. Just had the same problem, first was a loose battery connection so you may want to check that as well, but ultimately needed replacing of the entire starter.
the transmition is sliping
Your front end will clunck and bang and lock in 4x4,and may completely lockup.
The clunk is probably a universal going bad, and the popping out is probably caused by worn sifter bushings
The easiest way to tell is turn. Turn your front tires all the way in one direction and drive forward. If your blazer is in four wheel drive the tires will hop and cherp ect. Or turn your radio off and listen for a clunk when you push your 4x4 button on the dash. When engaging there will be a mild clunck. Hope this helps.