Bschweers

I resently installed Edelbrock headers on my 2001 Siverado HD with th 6.0 engine. I drove approx. 500 miles and now the runs alfull. Idles at 593 RPM and the listing from the OSBD II reader shows 15 degrees timing. It posted the code of D3900 mulitmisfires. I was talking to my parts guy at Advance auto parts and he was telling me that he ran into this problem before on the LT 1 with headers they found out to using a LT 4 sensors snd everything was happy. Does anyone know what set of sensors that are less sensitive (Part Number) that would clear my problem up. HELP!!