Geeezzz. Lot's of questions.

What it boils down to is, yes, you can use any chip you like, costom or whatever.
The benefits of the Extender are MANY.
First, it raises the air flow ceiling from 255gps to 512gps (or higher if you need it). Fueling in now controlled by the actual air flow and isn't "guessed at" using power enrichment tables.
Also, it is loaded with some pretty neat features that a lot of folks are discovering!
Anti Theft (with valet or convenience modes)
user selectable open loop idle
user selectable WOT TCC lockup (turn it on or off and select mph)
user selectable lean cruise (turn it on or off).
user selectable shift light (flashes SES light).
user tuneable spool fuel
Some other features I can't remember now off the top of my head. My cheat sheet is out in my car (tucked away for the winter under the cover)
The advantage of the LS1 (3.5") sensor over that LT1 (3") sensor is obviously the added air flow (if you need it).
Can a custom chip be made to read over the stock GPS?
Nope. Then it would be an Extender
