369k on the clock and I'm wanting some mild mods. Will this still leave me with a reliable truck or should I just leave it alone? I would like the highest fuel mileage I can get with a little extra power, nothing extreme. I'm getting about 16mpg right now running 295/75 bfg AT's What do you think?

First: Gauges!!!!! safety first
Then: BHAF, Quadzilla xzt+, boost elbow, 4" straight pipe, and maybe some RV275's

 

Those should be safe upgrade even with your high miles.

 

those upgrades sound pretty safe to me

 

I got my best mileage by far with a setup very similar to what you are talking about. I ran the Juice as opposed to Quads box. The power gains were very significant as well. The problem is after those mods you may find yourself wanting more. I know I did.

 

After the new wears off (hammer the throttle all the time) you should experience better fuel mileage. I experienced the best fuel mileage on my 24valve with a Van Aiken timing box, exhaust and intake, the guy I got the Van Aiken box from told me he was running 275's and he gained about 2mpg.