Cat mileage before plugged?

[torque]

My buddy has a '04 LLY with 50K miles. He thinks it doesn't pull a local hill like it used to. Anybody have experience with cat mileage/power loss???

[Kennedy]

Fuel filter is the first place that I would look. If the truck gets babied around town a lot it could start to soot up, but I haven't seen one plug yet.

[Mark Rinker]

Air filters can become salt encrusted and look clean, but restrict flow if they use salt on your roads
If its a daily driver that has become sluggish, put a load behind it and run a tank of well treated, clean fuel through it

[carco]

What Kennedy and MRinker said; by all means you have to chk or change the fuel and air filters first. The air filter is none too big, the capacity is minimal as related to restriction due to dirt plugging. The ACDelco filter does a very good job of filtering but total capacity could be greater. The fuel filter does a good job flitering and total capacity wise. Tire pressures, winter fuel and cold temps less than 30* do not help either.

My cat "fell off" and since then, last 19000 miles, has pulled 0.8MPG better per the DIC. Not much difference in normal driveing but when pulling the trailer, better mileage is noted. High engine loads breathe better with a less restricted exhaust.

[jmoser]

The catalyst on pre-2007 trucks does not get 'plugged' and this would not be the cause of any power loss. Those cats are very similar to a standard catalytic converter on a gas engine. In 2007 GM added DPFs which are a completely different animal.

[carco]

Just pulled a cat off a Power$troke that was about 75% plugged across the lead surface, no power in upper rpm's or on hills. Similar design internally to our GM cats.