1988 IROC Z 5.7 TPI Auto 2.77 stock engine and exhaust manifolds

It has always stumbled a little on startup but after a couple of seconds it runs fine

Idle is at 900

Timing is 6* BTDC

I have an Autometer air fuel ratio guage installed, at cruising speed it bounces between the bottom lean LED and middle of Stoich LED, at wide open throttle it will go lean off the scale (no lights) and about halfway through the powerband it will creep into the last Stoich light before rich.
It doesn't knock. I thought it was supposed to go deep into the rich range at WOT.

- no codes present
- It failed emissions once in January, I did nothing other than change the oil and then it passed.
- new EGR valve and it was an AC Delco exact replacement
- I have checked my vacuum lines several times and all have been replaced
- All my gaskets are new from intake at the egine to the top of the TPI
- Flowmatched stock injectors from Fuel injector connection
- tune up is getting close to two years old but the past year the car has not been on the road much as I was fixing other stuff.
- IAC is clean, throttle body cleaned, and TPS checked for correct voltage
- CTS for the computer is new

Basically I have slowly replaced most everything that could be replaced on this thing as it was a daily driver before my son was born

I am going top try and run through everything possible again this weekend.
Any ideas as to why it would run lean and what I should add to my checklist?
TIA

 

If it's connected to the stock narrow band O2 sensor, it's really not worth worrying about (or looking at for that matter).

 

Anyone know what voltmeter readings I should get from a good O2 sensor through the power band?

 

Time to step up to wideband if you need accurate data.

 

I understand that my guage is more a coarse information tool. But what my guage is saying matches the seat of the pants feel and the nose test on my exhaust.

Any other reasons that cause a lean condition? Something you normally would not look for. I am well versed on my car and the up and downs of my equipment.