Ok here goes.for two days I been chasing problems. We did a complete tune on a 2010 6.2 with a vararam intake and truck had no issues. Guy bought headers and installed em removed rear o2s and put front o2s into collector bungs and drove open headers 5 miles to muffler shop. Truck was running like crap on the way. After y pipe install and retune and deletion of rear o2s teuck feels as if its missfiring until you put it WOT then it hauls! Today I swapped out MAF,TB MAP,New plugs n plug wires,and rechecked AFR. Its not missing at all going by the scanner and will not set any codes! Runs like **** till WOT then it will outrun my 6.2 and mine runs 8.90. We put rear o2s in and let em hang bcause he doesnt have any bungs for em but it changed nothing. I found a cut and completely broken oring on the mass air n thought I had nailed it but it changed nothing!! Im lost no codes set, just runs like ****! Fuel pressure is at 50 till about 3k RPM then it jumps to 60. Not sure if thats normal but spec is 50-60 so didnt worry bout it. FP kinda fluctuated one time it was at light throttle at 60lbs and it was still running like **** so dnt think its FP. With convertor locked it feels just like bad missfires but loggs zero! Gimme some thoughts please. Thanks

 

Its so bad it will hardley turn gravel over at like 50% throttle in second gear then it kicks down to first n rolls out WAO!

 

Sounds like the front O2's are wrong, are you sure you didnt mix them up?

 

Bingo.

 

Never unplugged em.

 

The tuning section might be more help. Was closed loop disabled? If not, that could be the cause. You say that the AFR is good but how is it being checked/logged? Does the truck have a WB 02?

 

Check it with Lm1. Placed truck in open loop to rule out O2s nothing even changed 1 bit.

 

put the stock tune in it with the rear o2's turned off.
just to test, if it runs normal, it's a tune issue

 

what plugs?

 

Stockers at first then to tr55s nothing changed. We put stock timing table back in and no change and truck been runnin fine on this tune for 5 months.