hoping for some mpg help

do you need to purchase the xd-16 gauge? Or can you just buy the basic lc1 kit? sorry for all the questions i'm a newbee here. lol.

No... but it is very useful... You could buy the cheaper QB i think it is... as an alternative...

There are a couple of ways to command a "leaner stoichiometric" setting. Change the value in B3601, and/or change the O2 rich/lean switching voltage in B4105. In theory, since narrow band O2 sensors are essentially switching devices, you can alter stoichiometry by changing the O2 sensor reference voltage. I understand this has been done with some aftermarket controllers, but I can't confirm that.

I have had good results with getting rid of the IAT timing subtractions and the ECT subtractions as well---With the IAT deducts i will make all the table "0" up to 122* and then take out about 60% of the balance-With the ECT deducts i make everything "0" up to 205* and leave the rest alone.
Especially with the IAT what happens is that the sensor ends up reading underhood temps rather than intake air temps as the sensor gets heat soaked--espicially bad in city driving-- This also makes it easier to tune because when you ask for 20* you actually get 20*
Also you may get some false KR that will subtract timing--This is really bad on the E38 ECM's If I can't hear a ping or knock i will de-sensitze the knock sensors little by little til i hear it ping--then I'll go back some--
Also make sure your fuel trims are 0 or slightly negative just before going into PE--If you have a positive fuel trim the ECM will add that % to your fuel and will waste gas in PE--Also make your PE AFR richer than what you programmed in--
I haven't had any luck with changing the stoich AFR B3601 nor by changing the switching points B4105 lower---Anyone have any better ideas on getting the closed loop AFR leaner ? With LT headers , they always make the closed loop AFR richer, something like 14.0----Anyone know how to get it back to 14.68 ?????

Not sure Id recommend wiping the ECT and IAT correction out, I know for a fact that the TrailBlazer platform has MAJOR heatsoak issues, if you stop in traffic for 5 mins the IATs will spike a solid 10-30F, more with aftermarket CAIs. Not you go to mash the gas, tons of knock because the air coming in is much hotter. Right there you've got an issue, thats why GM built these tables in.

Yes you will get exactly what spark value you command, which is great for getting a solid baseline, but once you have your baseline you need to make sure the IAT and ECT correction tables are properly setup so if you encounter anything but whatever ECT and IAT values you tuned for originally you will have good performance.