This thread is full of fail. Your truck isn't running fine without the upstream O2 sensor, as it never reaches closed loop capability. Your truck isn't in "limp mode", it's in open loop and 30hp WILL NOT be achieved by installing an O2 simulator. The PCM needs to see input from an O2 sensor.

I suggest you fix the truck properly before you take it in, rather than ask us how to illegally make it pass emissions.

 

Fixed that for ya. The irony is just too darn funny.

 

Crap, I typed that between writing a paper for my Psych class, guess I should have payed more attention

 

Like I said! "rotflmao"

 

These are the parts I suggest to the OP:
http://www.summitracing.com/parts/MPE-23285/
http://www.summitracing.com/parts/NGK-23151/
http://www.summitracing.com/parts/NGK-23099/

Then you will never have to worry about passing emissions, and your CEL will be gone.

 

Good call on those parts, Purplage! They're what I've got on mine now and I'm shickled titless with 'em.

 

It is the same combo I have except for the sensors, I have Densos. I noticed a good gain in low-end torque when I put the Magnaflow on 4 years ago. And it sounds really good.