Start with the "hutch" mods to the stock fuel system See the article in the
TiKi Wiki The fuel system that is stock on the SD truck works well the biggest downfall is that it is a deadhead system so any air that gets into the system takes quite a while to be purged, which is what it appears that the driven diesel kit fixes. Their promotional information seems to sell the product more on fuel starvation to the #8 cylinder. While this is a documented problem; It does not appear to be a great problem for stock injectors, especially the smaller early '99 injectors that you have stock, even when the problem is present the impact is only realized when running 75% throttle or greater for extended periods of time.
The IDM mod will give you a bit more low end power.
The real question for you to answer is where do you want to end up? Would the fuel system be a foundation for more extreme modifications in the future? When you say "I want some more out of this thing" are you looking for more power to be able to tow faster up hills? Do you want some extra power when running around town empty?
In your position with towing power as the primary objective my order of upgrades would be as follows:
Better programs than TS generic
Injectors
Turbo
Larger intercooler
HPOP
Fuel System
The chip programs are listed first simply because it will give you the most noticeable gains for the money right now. If you have money available to do injectors or other modifications right now then get the chip programmed after you have those upgrades. Take a look at the posts from Tail_Gunner regarding his old truck his signature line will give you a pretty good list of mods to put on your wish list.
