The check engine light won't come on for something like a blocked air filter or squashed tailpipe. Both of which would kill power. There are many things that can kill towing ability without causing the check engine light to turn on.

Your tire size is close to stock and not enough of a diameter increase to kill power.

You say the power isn't adequate, but you aren't describing what happens. So really none of us can comment if the power truly down, or your expectations are too high.

If you expect the truck to pull 5 tons at 80 mph up a mountain, it certainly cannot and your expectations would indeed be too high. But if it can't haul a little trailer with 1,000 lbs of dirt above 40 mph on the flats, then it is indeed down on power.

Remember, you've got all of 190 horsepower. A powerhouse the T100 is not.