Unusually Poor Mileage

[Step'67]

Another mileage thread, I'm sure you guys are thrilled. Oh well, here we go. Maybe it's just me, but my truck has been sporting some pretty poor mileage since the trans swap/engine refresh. Here's my current setup: 355, 9.5:1, lunati voodoo 262 cam, vortec heads, performer intake, headers, glasspacks, edelbrock 1406 carb, hei, and a 4l80e.

Prior to the trans swap (and engine refresh), it had the old truck 4-speed, and was burning quite a bit of oil due to a bad intake gasket seal, yet even with this it still pulled 13mpg on average, driving spiritedly. Tore it back apart, bored it out a bit, decked the block, new pistons, brought up the CR to the above spec, etc etc.

So my question is, I seem to be averaging 8-10 mpg city, not much better if any highway, with the current setup, 10 being fairly rare. I just filled up, drove her pretty easy over the past week, 9.5 mpg. I've got a wideband O2 on it, and have the carb tuned to 15.3 afr on average for cruise, which is where it stayed this past fill up. Engine runs great, and timing was set up following the "It's just a pickup" thread. I know these things are like bricks dragging a parachute down the freeway, but come on... No fuel leaks to speak of, is it just that big trans sucking up all my gas?

Maybe I'm just expecting more than I should out of it, but any suggestions on what to try and bump up the mileage? I've been seriously considering megasquirting it with a 454 TBI that I already have, mainly because of the tuning capabilities it provides, and looks pretty easy to solder (do this for a living on cell phones) and tune, but also could I expect better mileage? Sorry for the long post guys, any thoughts? Input is appreciated, thanks.