Skipping and backfiring above 3K rpms ???
 

I know a little about engines, but sometimes I can't see the forest for the trees. So, I could use a little sagely advice from a pro or two about this.
My '98 blazer, when I accelerate a little hard, runs great until it gets above 3K rpms. Then, it stars popping a little (once or twice) shudders and starts accelerating fine.
At first, I thought, fuel pump. Because I've had some trouble with these fuel pumps on a few blazer. I've owned 4 and still have 2 of them. Looking for another one. But, I really like this one and have replaced the engine, rebuilt the transmission, and am still working a few other things (cosmetic).
Anyway, what do you think would cause this?
Any constructive assistance is greatly appreciate... Thanks in advance... :-)