Hey, I'm new here, and have a 92 IDI diesel with an ATS turbo. I was wondering what kind of performance mods are out there for a pickup like this? Thanks.

 

3 inch exhaust and a see through muffler is the biggest bang for the buck.
Another cheap upgrade is reworking the intake so it gets more air to the turbo.
Then you can turn the fuel up.
Set the timing to 7.5 BTDC.
Adjust the wastegate to about 15 pounds of boost.
All of these things are not very expensive to do at all, several just require adjustments.
When you want to spend lots of dollars you can do these.
Aftercoolers are kinda expensive, but help the power.
Propane injection is another thing that is kinda expensive, but I have heard good things about it.

The first thing to do is get a set of guages so you do not hurt the engine.
A pyrometer to monitor EGT is very important so you do not melt the engine, remember more power is more heat.
Before you can do anything with the boost pressure you need a guage to monitor what you are producing pressure wise, that way the heads stay on the motor with functioning head gaskets.

You may not want to do these things though, you may like it better than your Power Stroke truck when you are done.
You also have an ATS aftermarket turbo, do you already have the 3" downpipe and exhaust system?
Tell us more about what you have now and how you use it.