1999 Chevy 5.7 Vortec lean cruise help?

Hey guys and gals;
Summary first: I am looking for someone with experience tuning the later GMT400 platform PCM that is compatible with HPT. I?m willing to pay someone for their time if they are familiar and could help!
Details: 1999 Chevy Suburban 5.7 Vortec. No EGR w/long tube headers. MPFI injector upgrade. Fuel pump recently replaced. Runs like a top, but after headers I?m seeing a best of 14 mpg. I?ve seen 17 when stock. Power is up; less downshifts on interstate hills, but mpg is tough. Injector data has been recalibrated for the MPFI and stoich adjusted for e10. I am running 87 octane. Has anyone figured out a way to simulate ?lean cruse? like the Holden PCM in these? Or just peek at a log and tell me where I could improve? Driving 2500miles a month currently and would really appreciate any feedback! Just let me know what parameters you would want to see on a log and I?ll get it posted here. Thanks ahead!

Eliminating EGR on those is usually what hurts part throttle fuel mileage on those black box 5.7Ls in my experience.

I was afraid of that; but I?ve had carb fed rigs that got the same mpg and was hoping there was some ability in the pcm configuration to mimic a lean cruise like I can get with a carb and vacuum advance setups. I considered attempting a 16:1 stoich and using the PE tables and light throttle timing adder table to make it work but wanted to see if someone else had experienced success in lean afr with this pcm.

There is no lean cruise patch for the black box PCMs that I am aware of. I can lean cruise patch the blue/red and blue/green PCMs but even enabling lean cruise will not gain you 3 mph in my experience using it on my own vehicles to test it. I barely noticed any improvement other than it showing on the scanner that it was running at 16.0 commanded a/f and the O2s would quit switching and go to 100 mv or lower. You can try adding part throttle timing at cruise up to the point of it causing knock at tip in to improve mileage.

Ok; I appreciate the input. I?ve got it on the ragged edge with timing; 93 helps mpg by 1.5 or so when adjusted for it, but it?s not enough to offset the $1 more per gallon cost. I guess the easy button is getting a small car instead lol.

No EGR was +1 mpg on my 97 Express and a lot more part throttle torque. Fixed a bog off-idle that it always had from day 1. It hated the EGR because it was always wide open trying to accelerate from a stop and had minimal EGR flow at cruise. Lean cruise on the 0411/P59 was + 2 mpg. Tuned P01/P59 with a mild cam, thorley tri-ys, good exhaust and 4" air intake with a LS7 MAF had me knocking on 20 mpg highway at 75-80 mph and over 310 whp and 340 wtq. 4L85E transmission and 3.73 geared 9.5" 14 bolt at the time with 30.5" tall tires.

P01/P59 swap made a HUGE difference in the way mine ran compared to the junk black box.

Also FYI the PCM needs the injector data for the upgraded spider programmed into it either way. Made a HUGE difference in the way mine ran. I did the injector data and went to 14.1:1 for stoich to compensate for our 10% ethanol fuel and my WOT air/fuel ratio went from being 2 points too lean to nearly perfect on my at the time stock engine.