Trucks very sluggish when i begin to hit the gas. anfter a few seconds it begins to smooth out. Sometimes my check engine light will flast off and on also. any ideas? Bad coil pack? plugs? mass airflow? its shifts gears fine.

 

i would start with changing the fuel filter and run a additive to clean it out see if that changes it and clean the mass air censer , if that does not work maybe start with those other items

 

Start with what Dan said. If that don't fix it, check your other items in addition to the cat. A blocked cat will rob you of power therefore making it sluggish. If it's causing to much back-pressure then it can throw a code sometimes. I've replaced the cat, plugs, and coils on my truck and those made all the difference on my 2000 5.4