Thats good to hear on the mileage. What did it cost to add the blower/injector to your Tacoma ?
I bought the S/C from Toyota of Dallas online (back then, they were running a special at $1899.00, plus shipping). Since the truck only had 1225 miles on it when I had the S/C installed, I pony'd up about $425.00 to have my local Toyota dealer install it, so as to get it covered by warranty thru 60K instead of the standard 12mo/12K miles (quirk in TRD's warranty coverage).
I got the 7th Injector Kit from Toyota of Goldsboro for just over $1000.00, and since the truck now had just over 43K miles, I did the install myself.
At 48,500 miles, I had the S/C nose drive replaced under warranty at Savannah Toyota due to oil leakage (and probably broke even on the S/C dealer install costs as a result). I also purchased a set of TRD Headers at that time for $775.00 (dealer cut me a bit of a deal, since another customer had ordered them and then backed out).
Since I deployed to Iraq the day after I got the S/C fixed and bought the headers, I didn't get around to installing them for a little over a year <img src="/forums/images/graemlins/patriot.gif" alt="" />
TRD Headers and TRD Cat-back Exhaust (cat-back purchased on Ebay - I forget the $) went on at about 55K miles, and I again installed them myself, including the required cutting/welding on the front Cat Converter pipe/flange.
Since the S/C went on soon after the truck was new, I can't really speak to mileage on a normally aspirated 3.4L Double Cab. I added the 7th Injector to cure the pinging problem with the S/C (URD has a similar kit that probably works better for less $$, but the TRD injector kit is CARB-approved in all 50 states).
I don't think the headers and exhaust had much effect on my mileage, except that they sound great, so I am more likely to get into the blower as a result (mid-life crisis is in full swing! <img src="/forums/images/graemlins/lol.gif" alt="" />) Full boost gets you way down into the single digits on gas mileage, with a corresponding dent in your average mpg.
Two other issues you may want to look at: 1) there was a recall to place some additional shielding around the gas tank filler tube on some Tacos -- not sure if the 2003 is covered or not, but you should check. 2) There is a dash rattle TSB on 2001-2002 models (affects the mounting of the dash and the defroster duct), so you might want to listen closely over rough roads on a test drive to see if the 2003 has the same problem. I can email you a copy of the TSB if you get me your address.