Have you ever ran a vacuum gauge? At wot above 3500rpm it's starts pulling vacuum on the 305 tbi (never had a 350)that had the "ultimate tbi mods" and the "salad bowl", by 4000rpm I was seeing 3inhg.
Sure I only filled till the nozzle shut off (like everyone else), but I went to the same pump everytime, and recorded the trip meter and reset it everytime, I had a GPS that confirmed my Speedo was right (i did swap the vssb when I swapped gears) but sure I never had it taken to a shop to calibrate it like they do for police vehicles, it may or may not have been filled to the exact same point right down to the last drop but when the data I collected was being very consistent I don't see a reason adding risk of spilling fuel just to see it in my filler tube, which if you don't have a line that you fill to can be just as "inaccurate" and your vent wont work properly with it that full and on top of that unless you took the flap off the filler neck you can't even see in the tube.
And like I said agree to disagree, it can be hard to be told that what you believe in to be wrong. I only found out how much better the carb was by swapping to it (not my first choice but was the only choice I had in a short notice) I too did not expect it to drive the way it does and get the fuel economy it does.
This is getting off topic, the point I was making is The tbi injection system was a very inefficient design. if better fuel economy is wanted try anything else, carb is likely the easier to swap but going to a vortec with the updated injectors and a 411 pm to tune it in or to an ls would also get much better fuel economy