I just ordered some OBX long tube headers for my 2000 5.3
Ive been serching and found some diffrent results, but I concluded that headers are going to add airflow so the VE table will need adjustment for this.
The longtubes will move the narrow band O2 and screw up fueling even more.
Hopefully I can get a WB but not anytime soon.
After I install them I think im going to raise the ve about 6-10% and richen up PE to be safe.
I also heard at high rpms ve dosent really change but only changes some in the low and mid range.
Id imagine that the the NB O2 will be completly worthless indicating the trims becuase their going to be farther from the exhaust ports.