Lean AFR that I cannot richen up

[thehemi]

'99 S10 4.3 with SyTy turbocharger
Running (88k mi) 33# SyTy injectors

Idle, part throttle and minimal heavy throttle runs are great.
But once under load, 2nd gear accels, and it starts to reach
3,000 RPM and up, it leans out seriously bad.

I'm running a new Walbro 255 fuel pump. I just replaced the
fuel filter. And fuel pressure at idle w/ vacuum is 48 psi, and
58 psi w/o vacuum (in case that matters).

My PE tables are getting very high compared to stock, and it
doesn't seem to knock down the lean AFR at all.

At this point I'm thinking something else is wrong, but the only
thing I can think of is the injectors are bad. Does my situation
seem like a scenario for old, dying fuel injectors? I purchased
them used, supposedly "working fine" says the seller, and with
88k miles on them.

I have a new set of Mototron 60# injectors that I will try as a
replacement, but before I go through the effort I was curious if
my problem sounds like a sign of something else? Or if swapping
injectors seems like my best course of action?

[Bandit gs]

Check your fuel pressure when driving, my pump is dieing, idles fine, correct pressure, pull vacuum still ok, when i monitor it when driving it drops hard under boost. I also have a walbro, two years old, maybe 30k on it, i'm changing the pump in a few weeks when it comes out of storage.

I've smoked the vacuum system, no leaks, walbro had a bad batch of 255s about 2-3 years ago, I think mine might be one of them.

[thehemi]

Check your fuel pressure when driving, my pump is dieing, idles fine, correct pressure, pull vacuum still ok, when i monitor it when driving it drops hard under boost. I also have a walbro, two years old, maybe 30k on it, i'm changing the pump in a few weeks when it comes out of storage.

I swapped to my MotoTron 60s and the problem still exists.
My injector duty cycles went from over 100% down to 55%.
But unfortunately the injectors don't appear to be the issue.

Like you suggest, I'm going to connect a fuel pressure gauge
and monitor it while driving under boost to see what happens.
My Walbro cannot have more than 1-2k miles on it, but so far
that seems like the highest potential problem source.

Thanks for the reply.

[mr.prick]

You may need a new WBO2 sensor.