temporary loss of power

My blazer recently received a new fuel pump, a new computer, and a new spider. After about 30-40 mins of driving, it consistently loses power for about 15 minutes before it regains it back. When this happens the check engine light comes on. Also the blazer has absolutely no power. When trying to pass somebody the engine will go into higher rpms and will start to speed up only slightly. After 15 minutes though the check engine light will turn off and then everything goes back to normal. If in the middle of this i shut off the engine and turn it back on it goes back to normal as well.

Anyone have any ideas??? Im not too good when it sounds like the problem is something electrical/computer related.

Get the code/codes and post them back.
Is it losing fuel pressure?
Was the base time set?
How is the back pressure on cat?
What is the engine vacuum reading at idle and at 2k rpm?