I don't even know which motor mine has but it's a one ton 4 door 2003 with 323,000 miles I average 20 mpg. Wouldn't believe it if I didn't check it myself! Change the oil every 7500 mi, have put 3 water pumps, fly wheel, bearings in front wheels, 3 sets of shocks! Three sets of break pads.. It's a great truck!
Your truck has the 5.9 Common rail, but in 2003 there were three different versions, and 4 different transmissions.
From what I remember from 2003, here are the available combos.
235hp California, offered in a 5 spd NV4500, or 47re auto
245hp Standard Output offered in a 5 spd NV4500, or 47re auto
305hp High Output , only available in 6 spd NV5600, or 48re auto
