I installed my long tube headers last night in my 2008 silverado 5.3l flex. Now it's saying reduced engine power and the check engine light is on. I had the battery unhooked when I installed them and I hooked up my o2 sensors. It had been tuned by Texas speed b4 I installed them. Any ideas on what could have happened?

 

check your connection to the throttle body. ive heard that a lose grey wire or any wire within the plastic connector can get loose and break. do the pull test on all the wires...