Pyrometer first. Use it to verify that you aren't operating on a sustained basis (towing) at more than 1200 to 1250 EGT (exhaust gas temp).
There is infinite info out there about how to make more power, but about 10% of that info is practical for someone who actually uses their truck. The general formula is as follows:
1. Improve exhaust system. Remove restrictive items, and provide a free and open exhaust path. What you need to do here, may differ from what the diesel shops want you to do. If you have 3" minimum downpipe, 3.5" minimum exhaust piping and a relatively free flowing muffler (example Walker BTM muffler), you're good to WAY more power than you can tow with at safe EGTs using the factory turbo.
2. Improve intake system. Lots of folks put in a 6673 size air cleaner. You'll have to research your rig to see if that's needed or not.
3. Add fuel - you should be able to tweak (mech injection pumps) or tune (yours) your way into more fuel, even with stock injectors. You can quite likely add more fuel with your stock injectors than your pyrometer will say is safe for towing.
4. Improve turbocharger and exhaust - you can change to a borg warner SXE series turbocharger and a full 4" exhaust system, and move more air. This will help mitigate high exhaust temperature. However, from off-idle to about 1500-1700 rpm, your factory turbo will probably make more power with less smoke than any recommended aftermarket unit. With a turbo swap, expect to have a more peaky engine that starts making good power without smoke at 1500-1700 rpm.
5. Once you have a better turbo, then you can chase more fuel with injectors.
6. Repeat 4 and 5 until you are broke, or the truck is broke. Twin turbos, head studs, low pressure fuel system improvements, big injectors, etc. and so forth.
You'd probably have a pretty satisfying rig with steps 1/2/3, without spending much dough.
