05 Suburban Z71, 5.3, auto, 4x4, 111k miles. Had the trans serviced last week. Asked the tech to scan my check engine light. He said O2 sensor. Yesterday I replaced all 4 O2 sensors, plugs (NGK Iridium, had ac delco) new wires (MSD Custom). The pre cat sensors looked perfect but I noticed the post cat sensors had carbon build up about 1/3 the way from the threads to the tip. Also the check engine light is blinking and it never did that before. Car ran great before, started after tune up and it idles rough, shakes, and just runs like crap. It doesn't want to accelerate but will and smooths out after 2k rpm. Backfired on decel twice.... I didn't touch anything to cause this to happen, can't figure out what the problem may be. Also, I just remembered, the exhaust smells bad.

 

Welcome to the forum. If it ran well before your work, go back and verify that what you replaced is correctly hooked up.

 

I tried the NGK Iridium in mine, rougher idle, pulled them and put the AC plugs in. NGK didn't have as much tip extension as the AC's.
AC run best in GM motors. I use NGK in all my sleds and other small engines with zero issues but my Tahoe didn't like them. Also there are a lot of knock off parts out there including NGK plugs. Where you buy them makes a big difference.
Blinking CEL is a misfire being detected, do not drive it as misfires will dump unburned fuel into the cats and kill them, that's why the blinking CEL blinks as it's a warning not just a less serious code being set.