acceleration problem

I have a 2000 full-size Blazer and I am having trouble accelerating on occasion. It only happens after I first start it and am pulling away. It sputters and chokes for several seconds before it finally starts operating normally and I can go. It then runs normally until I shut it off and start again. I don't understand why it would do this after I first start it, but then run normally the rest of the time. Any ideas?