2006 Silverado HD 6.0l

[Thomas.berry13]

Serious power issue. Engine load is running 26% at idle and sluggish while driving and random misfires occasionally but absolutely no engine light/codes!  changed the map sensor, plugs/wires, new cats, new muffler, new knock sensor/harness, new purge valve on intake, new fuel pump/filter, new transmission. Im at a complete loss of ideas. Anyone know why this thing keeps dragging along.with no codes or explanation?

[davester]

wow.  that's a lot of expensive parts to throw at it.  did you try any diagnosis, like looking at fuel trims, checking for intake/exhaust leaks, looking at sensor data from the MAF, knock sensors, O2 sensors?  And are you getting the correct fuel pressure (new part != good part)?