Do you have a SES(service engine soon) or CEL(check engine light) hooked up? If you are running a stock computer,and no cat,and no 2nd O2 after the cat,you are going to run pig rich. You NEED that 2nd O2,and if you are not going to run a cat then you need this
http://www.gtimotorsports.com/product/O2-Sensor-Spacer/Default.aspx?gfid=p653 or something similar to "trick" your ECM.