I had the same problem, bought the truck like that actually (2K blazer 2 door 2WD 4.3) made it really dangerous pulling out into traffic! but thanks to this forum, figured out it was a dirty MAF sensor. here's a link to a great way to clean it that will save you about 80 bucks in mechanic fees.

K1500 P0171 P0174 Fix How to 5.7l - YouTube

I did it the same way he does in the video, now my baby rolls hard! doesn't take much to light up the tires now! its like a whole new truck best of luck every 1.

 

Glad to be of assistance