im going to just back up what everyone else said...the 3v came into the in 05... as far as MPG...my dad cant break 11 mpg in his v10 where as i just got 13.5 with mine and that wasnt ven babying it...we drive the same route all week....if you tow heavy loads...yes wait and get a v10, but the 5.4 is a solid motor even though pre-05 models were a little under powered...as a everyday driver and a once in a while tow-rig, the 5.4 is a great little motor...paired with 4.10 or 4.30 gears it would do just fine...keep us posted!!!
1999-f250/f350 5.4 (2v) - 235hp and 335 ft/lbs
2000-2004 f250/f350 5.4 (2v) - 260hp and 350 ft/lbs
2005-2008 f250/f350 5.4 (3v) - 300hp and 365 ft/lbs
1999-f250/f350 6.8 v10 (2v) - 275hp and 410 ft/lbs
2000-2004 f250/f350 6.8 v10 (2v) - 310hp and 425 ft/lbs
2005-2008 f250/f350 6.8 v10 (3v) - 362hp and 457 ft/lbs
That looks like a good old wiki quote, the SD's never had the NPI 5.4L's so the '99 numbers are wrong. Not to mention I have never heard of NPI V10 heads which is what that 275hp number must be trying to say.