Hello all, I'm new around here, but would appreciate any help I can get with a problem my Blazer has been having.

Once the truck is all warmed up, usually after a long drive (through traffic mostly), if I come to a large hill I will be accelerating up the hill and SOMETIMES it will feel like I lose a good percentage of my power. It hasn't happened many times, but enough that I have noticed. One time when this problem occured my check engine light started blinking, but cleared as soon as the hill levelled out.

I know that my tranny is fine, as I just got a new tranny installed. I assume this is a ignition problem, but am not certain. Any info anybody could give me would be great. Thanks!

Replace the fuel filter before you do anything else.
Going up a hill(engine under load) and loosing power is a clue that you are loosing fuel psi.
I would bet if you ran the code it was for a lean o-2 sensor

Go to autozone and have you codes scanned and come back here and list them for us.

We need the codes, not the description.

Autozone will read you computer and give you the codes for free.