Diagnosing an Avalanche

[BBA]

Trying to help a friend with his 2002 Avalanche 5.3l with 40 K miles. The symptoms are it starts lazy, takes a lot of turning over to start up, but it does fire up smoothly. It's been doing this for about 8 months.

It runs nice and smooth, although IAT's get a little high in 90-100º weather.
It has no DTC's, so I figured I'd log a drive and saw some rather weird stuff happenning.

Everything looks good at steady cruise, but on ANY and I mean ANY throttle transient, accelleration from light to full throttle, the LTB1 reading instantly shoots as high as it can go, then as low as it can go, and stays like this until he lets off the gas. The LTB2 acts normally, slight variation, nothing to speak of. Everything else seems normal.

The O2 B1S1 reading goes crazy as well, cycling much faster than the O2 B2S1.

I'm going to change the plugs in it tomorrow and see if they make a difference but WTH?

I could understand a misfire from a soaked plug, or even flooding from a leaky injector maybe but no DTC's at all???

Any ideas?

[Hauss]

can I see the scan and tune?

[2xLS1]

Check the fuel pressure regulator for a leaking diaphram.

[BBA]

The tune is stock and here is the only scan file I have so far, just happens to be the one when it was 100º outside.

[BBA]

The problem is weak plugs. The LT problem was worked out by tweaking the charge temperature coeficient tables.

Should have known by the lazy startups...always do the simple stuff first (plugs that is).