I would change them out, I've fixed many poor fuel mileage complaints over the years replacing old, original o2's. Just because there isn't a code don't assume they are fine, they can get lazy and not throw a code. Especially if you can do your own work, for $200 its a good investment.

 

With the right software, you can monitor your O2 sensors to watch how fast they are switching to get a feel for their condition. If they are switching slow I would replace them, but at your mileage I would expect them to have deteriorated performance.

 

All I have is an actron scanner that's shows a few things other than codes such as tps%, IAT, O2 voltages. Is that enough to look at the way they are acting?

They look like they fluctuate a lot WAY up and then WAY down.

I guess I'll be replacing them and fixing a spark plug hole and see how that goes.

 

Replace your intake manifold gaskets.

 

I might be a bit dumb here, but what makes you believe I should replace intake manifold gasket?

I've recently sprayed carb/choke cleaner around the intake and vacuum lines after I had to pull the heads to fix some broken bolts. No RPM changes. I was told I could use 98-02 LS1 head gaskets, they were cheaper so I did use them, could that be a problem?

 

The intake manifold gaskets on these engine have a tendency to compress and not completely seal. Usually its on the underside and is not always detectable by spraying solvent.

Gm switched from the orange o-ring material to a greenish blue color because the material is more resistant to today's gas with higher ethanol content.

Pay close attention to the o-ring material on the intake gaskets. If it's compressed close to the plastic its bonded to, then they need to be replaced.

 

I'll probably be getting new gaskets soon. Does the torque sequence for the truck intake match the sequence for the LS1 intake, per instructions from LS1howto?

I did fix my exhaust leak at the header to cylinder head and it idled and sounded so much better. Still wanna do sensors and tune. Gotta get to the track and see what this cam and headers will do for me!