Finally finished long tube install, have a few questions...

I installed a Spec stage one myself about two years ago and it been great so far, no issues what so ever. As for the check engine light, be aware that MIL elimantors dont always work. I tried two different sets with my Catted Xpipe and neither would turn the light off, I ended up going with a chip.

i remenber hearing that since on LT, it relocate O2 senser down farther, exhaust gas would cool down and turn the SEL lights on. if that is the case, u might wabt to wrap ur header, and try to contain the heat

You're check engine light is probably on because of the front o2 sensors. MIL eliminators aren't going to help you in that case because they only keep the rear o2 sensors from tripping the SES light, they just trick it into thinking the reading is normal because rear o2 sensors are pretty pointless. The front o2 sensors is something you would might want to consider getting a really good tune for. Like what was said before, those front o2 sensors are pushed further back from the engine by the long tube headers, so the air is going to be cooler than what it was with the manifolds. I don't think header wrap would help, you could try it but I've only heard bad things about it.