99 C3500 W/7.4 Questions

[96chevy7.4L]

Hi guys I have a 99 Chevy C3500 w/ 7.4L vortec aboard. I was thinking of going to set of the gibson truck headers with the 1-3/4 primaries whcih is about standard for a big block. But my question is will going to a set of headers cause any issues with the computer? Will the oxygen sensors not like it or will I have any problems at all. I know the headers will help it evacuate the exhaust better and decrease under hood engine heat. I have a 50 Series Blig block muffler on it from Flowmaster. It uses two 2-3/4 inlets and a 3.5 inch outlet Next and last question I was going to get a blackbear tune in July will this be a benefit for that as well. Any opinions or ideas appreciated.