4wd question.

Ok, I have an 89 S-10 blazer, and when I take off from a stop in 4wd, it doesnt go right away. Theres a delay after I hit the gas until the car moves. Its getting gas, and the RPMS go up, but it almost feels like somethings slipping ? It kinda jolts forward when it catches, and its not that long of a delay, like .5 -1 second, but noticable. And it only does in in 4WD. Any ideas?