Surge at steady cruise & little lope at idle (SOLVED)

[Kc5khr]

I'm looking for some new ideas for trouble shooting a 2003 Tahoe I recently inherited. It is a 5.3 Flex Fuel with 207k miles.
It has a soft miss at idle and has a mild surge when at a steady cruise speed. Acceleration is good and starts up instantly.
New parts...all Delco, Delphi etc..:
Plugs
Wires
Air Filter
Fuel Filter
Intake gaskets
Fuel Filter
Fuel pump
Throttle body looks new, but Chinese

On my basic scanner it looks like O2 sensors are swinging normal, short & long term fuel trims look good, TPS (pedal) sweeps smooth, MAF graphs good, no strange engine noise, no CEL or stored codes, hot spark at each plug and all injectors firing.
It doesn't matter what gear you are in or rpm, once leveled out at a steady speed there is a slight surge, almost like it's running out of gas.
I have an injector pulser on the way to do a balance test and going to check for clogged cats, but as good as acceleration is and don't think that's a problem.
I have a fair amount of experience with OBD1 stuff, tuning, datalogging & burning chips but this one has me stumped so far.
I don't have equipment to dig any deeper...yet.
Any ideas are appreciated.

 

[Kc5khr]

Forgot to add, no smoke from anywhere and I've just started closely monitoring coolant level. It was at normal level when I got it and hadn't needed to add any so far.

 

[Fless]

Inspect the wires that connect to the throttle body. They've been known to break under the insulation within a foot or two of the TB, compromising the wire. Have you done a standard vacuum check?

 

[Kc5khr]

I'll look at those wires. Vacuum test is good. I went ahead and ordered a fuel pressure regulator as specs are all over the place for the flex models. Not having history, I replaced the fuel pump for reliability reasons. Key on engine off I had 40lbs, new pump has 41. It is a couple of lbs lower than spec, but I'm not thinking the regulator will fix it.
Thanks for the suggestions.

 

[Fless]

Fuel pressure is too low. KOEO spec for the 5.3L Flex is 48 to 54 psi. I'll be curious to know if the FPR improves it.

You may want to use a fuel pressure gauge on the fuel rail, snaking a long hose through the hood gap so the gauge is where you can see it while driving.

 

[Doubeleive]

fuel pressure should be higher for sure

 

[Kc5khr]

Update....Installed new FPR and had no change in fuel pressure. I have been told by some, on the Flex Fuel models WITH a rail mounted regulator, the correct way to check the pressure is when the engine running at idle and the regulator vacuum unhooked. With this test I have 50lbs. I feel like everything is good with the fuel system, since everything but the lines are new. To test potential pump pressure output, I slowly restricted the return line and could quickly produce over 90lbs on the rail.
I borrowed a device to do a little more advanced testing. The first test (I think Power Balance) where you cut off fuel one cylinder at a time, was passed. Big difference when each one deactivated.
I then did the injector balance test. Had less than 1lb difference between all injectors.
One thing I noticed on the scan tool is MAF swung between 3 & 6g at idle. Is this normal?
I did a short drive with the MAF unplugged and still surged.
Also noticed longterm fuel trims were around -9. Short term alternated from -3 to +3.
Have a solid 20" vacuum on gauge, shown as 10" on scan tool. Had to think about that one for a minute.
I did another carb cleaner spay test on the intake anywhere there could possibly be a vacuum leak.
Before I got the scan tool, I had ordered a Delco throttle body to replace the Chinese one. Numbers looked good on the scan tool, but I'll put the new one on anyway.
Also checked for clogged catalytic converters, with a temp gun. If I remember I had around 425F at inlet and 500F at outlet.
The little vibration I have at an idle is more like something out of balance than a dead miss and I still have the mild surge at steady cruise.
What else am I missing?

 

[Doubeleive]

@swathdiver

 

[exp500]

With FPR unplugged does it still miss/shake at 50#? Is fuel leaking thru vac line FPR? LTFT idea.

 

[Kc5khr]

Still has the mild shake. No fuel in the vacuum line.