What motor and combination is this? Need more info
I always ran the wideband 12" from the turbo
Any kind of air leak in front of the sensor will kill them. The sensor should not be after a gasket transition to the main exhaust.
If this is a turbo LS your exhaust temps are likely too high because you are running too LITTLE timing and too much fuel. There is also a possibility to hurt the motor running too rich just as too lean.
If you post your tune and it is either MS3, hptuners, or holley I can try to help you
TIMING POINTERS:
Cruise and low map
1600 rpm 30 degrees
1800 rpm 32 degrees
2000 rpm 34 degrees
2200 rpm 36 degrees
2400 and up rpm 38 degrees
Peak torque/mid throttle
I don't know what system you are using but his should be 15-20 degrees
Full throttle and anything slightly below boost to slightly above boost should be your normal NA timing. For some reason there is an urgency to turn the timing way down with a turbo everywhere. This will make the engine super lazy.
5500-6500 rpm 26 degrees on a turbo LS 90 map to 110 map or PROBABLY .56-.68g/cylinder airmass in hptuners
From full throttle your timing should blend down to hit 14 degrees at 14 psi - yes this even applies to pump gas.
You should not be running 9-10 degrees unless you are running 18-19 psi of boost, at which point this isn't a pump gas deal.
AFR POINTERS:
Most cammed LSes like to idle/return to idle at 14:1-13.5:1 AFR.
Cruise you should just run stoich or if you have E10 gas then 14.2-14.3
Anything mid throttle should blend to 13.5
Full throttle, yes even with the turbo, should blend to 12.5:1 once again everywhere from 90 map to 110 map. You do not need to go hugely rich at 2 psi.
Your AFR should blend down to 11.5:1 at 14 psi. If you are a super safety master you could blend to 11:1. Some combos just will not tolerate this though.
I would not blend to 10.5:1 unless running 20 psi, and that blend would only start above 14 psi.
SPARK PLUGS
Run the ngk tr6 at .025 gap for 14 psi and under. If you are "blowing out the spark" - which is a high rpm hesitation or shudder with lots of soot then you can try an even tighter gap.
Run the ngk br7ef at .020 gap for 15 psi and over
SCENARIOS FOR POOR HIGH RPM PERFORMANCE
If you take a 4.8/5.3/6.0 or an sbf 5.8 and you hit it with 4 psi of boost, richen it to 10.8 AFR, and cut the timing in half it may make less power than it would N/A with 12.5:1 AFR and full timing. I have seen this in cars I've tuned.
Once again, I don't know your combination, but watch Richard Holdener's youtube videos where he compares the same turbo on different size engines. He has a video where he runs the ebay gt45 on a 4.8 and a 454. The 4.8 makes more power. The smallest engine that can max out a turbo in its useable RPM range will have the least back pressure, the best power curve, the most controllable boost, and make the most power.
I see a lot of guys who want "ultimate boost response" put the gt45, the 7665, and the small a/r 7875s on 5.3s, 6.0s, and 351 fords and they are dogs up top - too little turbo for the engine.