efans are a good upgrade for a turbo kit

 

You wont really see any gains from the efans, makes the motor spin up slightly faster! and the A/C cooling off faster < haha so true

efans probably free up 10ish hp at the crank which is like 5-8 at the wheels. Don't believe the efan company's 17-25rwhp gain BS.

The best thing to do would put some 3.42s in except your truck weighs so much that it would probably wind up hurting the mpgs due to bogging.

You could put some smaller wheels and tires on the make take off smoother, but on the high way the smaller wheels will be turning faster along with the rpms.

A cam with a high lsa and releases cylinder pressure would help mpgs some.

15/16 mpg for a 2500 is pretty good and the problem is trucks weigh so much and push a lot of air = crapy mpgs

 

you getting 15/16 your doing dam good

 

I'm running 285s and I don't want to go smaller because I feel the truck would look funny, and I've heard of people swapping the cam and seeing better mpgs

 

If all you're after is great gas mileage, keep your tires at 35+ psi, don't run the ac, drive 60-65 on the highway, lose any excess weight, and get a reputable tuner to get your truck dialed in.

 

And change your spark plugs and front O2 sensors if you haven't in the last 20k and 60k miles, respectively. The O2s are good past 60k miles, but when I changed mine at about that mark, I picked up 1mpg and the truck felt a bit peppier. Get AC Delco from the dealership, don't go cheap on these with an ebay pair or Bosch, you will replace them again if you do (ask me how I know)

 

I have 3.73 gears, and 285s on my truck also. 50 up front and 45psi on the back
When I had a the NNBS style intake, 224/230 .591 .592 -110 and full bolt ons it was 17-18 at 65. I do lots of freeway driving at 80-85, and I was getting 15-16mpg

I did the L92 heads/intake swap, TSP Torquer V2 cam and there was hardly any change

The only way to get better gas mileage, is to park it, or drive 65

 

An under drive pulley did not help either, It made the motor spin up "slightly" faster, but was a total head ache to install b/c I didn't have a special press tool. Eventually it walked it self forward some what and made the belt chirp so I put the stock one back on. The one upgrade that gave me nightmares!

 

I get 14MPG out of my CCSB 2500HD, with synthetic front diff oil, t-case and transmission fluid. It seemed to help it roll smoother down the road, but I doubt it contributed anymore than 0.5MPG and no more than 1MPG. I'm sure just replacing them with new fluid would have helped out even slightly.

I did like what the AMSOIL universal ATF did with my 4L80E though, it made it a much smoother, quicker shifting transmission. It also made the 4WD engagement in my NP261 much smoother, especially on -40* mornings before the engine even warms up. I could shift from 2HI to 4HI with two fingers, before I had to push and pull on it to engage.

 

An alternative for you would be 255/85r16's they are quite a bit narrower and the same height. I wouldn't go switch them out or anything, but maybe look into them next time you get tires. The problem with that size is there aren't many companies who make them. But on the bright side, you can use one if your old 285's as a spare.