and i also replaced the timing chain and mapsensor

 

If you have an autozone or another parts store that will read the codes get them to read the code and give you the number, it could be that you got a bad 02 sensor and its making it run really rich

 

try to read the codes with the key dance. on - off - on - off - on.

 

i can never get the key dance to work for my truck. Ya i will go by advance and let them read it. What are the chances of a new sensor being bad?

 

well its not that common but it is possible

 

Key dance doesn't work on '99's.

 

True duals should really have an X pipe within reach of the upstream o2 sensor with the sensor in the center of the X.

Like this one
http://www.summitracing.com/parts/MPE-10791/?rtype=10

 

A bad code from the upstream sensor is probably your culprit.

As far as running rich from better airflow and less backpressure, I rather doubt it. I'm running a CAI, LT Headers, a Magnaflow Y and Cherry Bomb Extreme and along with my SC tuner advancing the timing, I had to install a 180* thermostat because I was running too lean...