Just to recap, when he left here the tune was shifting fine, it wasn't until later when nitrous was installed that the shifts were holding too long.
unfortunately, with the 6speeds, they cannot be tuned remotely due to the controller being internal to the trans.
ya, he had some o2 related issues as well, that causes it to stumble and not run correctly, i've seen others post about this as well, picky o2 sensors.
All NNBS sensors are picky. My knock sensors have picked up KR for the last 8 months, even on a bone stock tune and 91 octane.
1969 Chevy RCLB C10 350/TH400 SOLD
2007 Chevy RCSB 4.8 4x4 LS SOLD
2008 Chevy RCSB 5.3 4x4 LT SOLD
2010 Chevy CCSB 6.2 4x4 LT SOLD
2005 GMC CCLB DRW 6.6 Duramax 4x4 191,000 and counting
2013 FORD CCSB F350 6.7 Powerstroke 4x4