2500HD Clean up

[Kubaner]

Hey Forum, I'll be as short as possible and apologize in advance for asking about something that I'm sure has been answered many times before.
I've got a 2004 Sierra 2500HD with 100K miles. Just made the decision to keep it for a few more years and want to do a handful of things to it to clean it up and make it last reliably. Other than routine maintenance and a set of 285's on it I've pretty much done nothing else. Torsion bars are cranked up so it's pretty level. What I'm looking for is your advice on what I should have done to begin with and will do now once I have a plan established. Really anything you guys think is a necessity with this truck I'd love to hear about.
I need shocks and would love to see the truck a little higher but don't see any real need for a true lift. What do you think the best key/block/leaf setup would be to improve the trucks look? I could see bumping the tire size up a bit too if they'll fit. Again, I'm not looking for 35's and 6" but somewhere in between cranking the bars and a full lift.
What would you do to improve the gas mileage? Chip/computer/air box, etc.
I do have a couple exhaust leaks so I'll more than likely be doing a partial exhaust replacement and would like something that sounds good but not too grouchy.
I know the brake lines and exhaust studs are known to fail frequently on trucks this age too. Mine appear to be holding in there though.
I know that torsion bar threads are everywhere on these forums and I'm not looking to avoid doing my own searches. There is just so many that by the time you think you've figured out what's best someone else says something different. So hopefully if some of you have time and can throw me your 2 cents and a few more of you agree with them then I'll have a good direction to head in. Thanks for your help.

 

[Z15]

If you keep going to bigger tires your mileage is going to get worse as you are changing the axle ratio and that in turn cause the engine to operate outside of its designed torque limits, trans to shift at what it thinks is the correct rpm but the tires are fooling it. Also, the larger tires add more rolling resistance (friction) and weight to haul around.

Changing the air filter or the air box is not going to result in improved mileage, the computer is programmed for so much air and you cannot change the computer code but adding an air filter. The idea these air filters and cold air boxes improved mileage on computer controlled vehicles is all designed to sell these items.

If you got 100,000 miles you should change all of the auto trans fluid. The service life is 100,000 at best.

Its not very realistic to think you can gain a lot of mileage in a vehicle that weighs between 5,000 and 6,000 lbs. That's a lot of weight to propel down the road. Look at all the econobox's out there, they are light weight, small engine and small tire vehicles.