well its been almost a year and here are the results.
got rid of the 37/13.5/17's and used my blazer tires which are BFG mud terrian KM2's 35/12.5/17's
instantly saw 2 mpg difference.
then did the AFE cold air intake AFE mouth Piece, 4 inch turbo back exhaust with muffler.
Edge juice with attitude CTS.
ran it thru all the levels and for a month on each. mix of city and driving. found the best option for me driving like a grandpa is mixed highway and city level 1 which would get me 18.2 mpg hand calculated over many tanks.
from north denver to trinidad doing 65 instead of 75 on I25 i was able to get 19
as for power, had it dynoed with the mods when it was on 37's at the rear wheels it made 398 HP and 705 Ft lbs of torque on level 5 (did not do the hot unlock)
have not dynoed it with the 35's yet.
as for maintence, it now has 16k more on it since i bought it. i had to put a water pump, driver side hub, new batterys,
this week i need to replace the pass side hub, needs both rear axle seals and possibly the pinion seal, also the transfer case rear output seal, and needs shocks.
overall after almost a year. im still loving it. hauled a couple trailers no big deal. had a 24 inclosed trailer loaded full that i hauled to trinidad when i moved my buddy, ran 75 all the way and got 10 mpg. there are some long hills down by that way (not huge like if going over the mountains but still a good climb) and it ran 75 all the way and would have held 5th gear with no problem but i dropped it to 4th just to be safe.
my dad has a 05 6.0 with the 4l80 in it. towing of course is a big difference compared to his but also just driving around town its amazing how much the drivability of the duramax is better than the 6.0.
anyway thats the year update. highly recommend the DMAX, even though i have had some small mechanical issues.