If you had an underdrive (or lightweight) pulley on for the earlier
runs, and went back to stock for the other, that probably
IS why you lost 6-8 ft lbs.
If you kept getting CEL with the underdrive pulley...just go
with a stock diameter lightweight one.
You'll get 80-85% of the power gains, but without any of the underdrive
pulley drawbacks...and therefore probably no CEL's.
LW Crank pulleys are a cheap ($125) way to get more power to the wheels.