to start i have a 96 blazer with a transplanted 4.3 from a 2000 blazer. untill this problem it was working great . it had a problem on the feeway severial weeks ago. i was accelerating and it made aloud poping noise i did not notice a proformance isue at that time. when i got off the freeway and stoped at a light then it was, and still is having trouble idleing. and sounds like it is missing ,and thru a code p0106 i found when i got it home.

checked for vac leaks and could not find any.
checked out the map sensor it functioned normally.
checked out the plugs did not see anything real strange but large gap on several . i felt that new plugs were needed . no change.
also changed the fuel filter. no change

checked out the fuel pressure and it was 50 psi so i thought that the fuel pump was bad. and changed that. that made no change. still 50 psi.

checked the leak down test and it will hold the 50 psi just fine. not sure where to go from here.
any help would be appreciated