post #4 is very true; I'll attest to EGR on my TBI-L31 (it's worth using). Hard to say mileage increase is "substantial" or even real, but I'd say it's totally plausible. My motor pulls way harder with EGR open at light throttle. This is from extra timing; with less fuel at the same time, the motor is operating more efficiently. Doing more timing and less fuel without the EGR open is playing with fire; I did get pinging when I tried this for shats and giggles (went away when I plugged the valve back in).

Toying with EGR can be amazing, you'll feel it if you get aggressive in the tables. I find it's safe to have 38*-39* total timing, or more (L31-tbi). Safest to simply set this limit with the 'max timing' constant. I had some evil noises with 41* and 20% fuel reduction, YMMV. Leaning out by much more than 15% noticeably reduced power, so I stay around 15% max and I have no problems maintaining speed up slight hills without going into PE. The vortec heads seem to love the extra timing when EGR is open. If I set EGR to come on only above 60mph, it's a world of difference on the highway when I cross that threshold.

In $0d, you can tune it to come on/off based on many parameters, you just have to use good judgement. I don't recall a flag that disables it explicitly for PE, it was based on MAP values and TPS.

I patched $0d_maf to include EGR functions, but I haven't extensively tested it yet. I kept having unrelated issues using MAF at low rpm under load in 4th gear. I suspect I need an intake 'reservoir' like on the factory vortec intakes. PM if you want $0d_maf_egr.asm, I'll share if I happen to notice your PM.. (i'm also on FSC)