Need Help: 350 TBI Running Rich/Bogging

[RUN GMC]

I recently had the same problem on my 87 replaced everything except the spark plugs wires which in hind sight I should have done first but since they were not really old (14 months).....so I decided to replace the spark plug again and I saw only 3 spark plugs were fouled somewhat compared to the others (and I had laid them out in order to know what cylinders they came from)....after replacing plugs I started up the engine and noticed I had the same bog down and a slight miss....at this point I removed and replaced the 3 spark plug wires for cylinders that had the fouled plugs.....upon recranking it up I could tell it sounded better and it pulled better but I also read that it takes 40 cranks cycles to get the ecu to dial in the parameters to make it run really great again.....hope this gives you food for thought.........