computer says cats..2006 nissan titan..lost allmost all power and runs like crap..tuned up

Replace Catalytic Converter. Its probably all plugged up by this time.

Be careful. My 2006 Armada has 4 Cats on it. At 155k miles I took it to the dealership for the problem, after trying to replace my fuel pump for $800, the decided instead to replaced the front two cats ($1,700). 1,000 miles later, had same issues and they replaced back two ($1,300). In the meantime, the "crap" from the exhaust was backing up between the front and rear cats and being recirculated through the engine via the EGR valve. When I took it in, I had no issues, no oil consumption. After this ordeal, I am burning a guart of oil every 100 miles. Now they say cost will be $8,000 to install a rebuilt motor. Offered trade in on a new Armada at $5,000. These guys are clueless.