Siggy

I have a 88 TPI 5.0 R700 165 ECM.
I've pulled the AIR+EGR and fitted KN filters and Crane CDI ignition, After these mods fuel consumption was like 10-11 mpg mix driving. After reading the threads I started diy prom burning over 3-6 months without effecting my mpg but the engine was strong, I used a slightly modified ARAP bin. My plugs were gapped at .050 and ground the earth arm to center over the electrode.
I assumed that 10mpg was permanet, however after 6 months driving without altering the eprom I stupidly lost my ignition module (voltage spike) and replaced it and new plugs gapped to .035 (standard electrode) as recommended in the Crane ignition manual. Well surprise...my mpg is much improved, 15-16 mpg mixed driving. Now I know the BLM learning is there but a mpg change like this seems a bit much??, and the engine seems very strong and sharp. I have not as yet logged the ECM, can anyone make logical sense of this?