It seems like the easiest performance mod is to replace the air intakes with a cold air intake system. There are several available, and go from serious D.I.Y. style to simple bolt-ons. The key there is to reduce the disturbance of the air flow, while sucking in cold air, and opening the restrictive OEM inlets. I haven't looked at all of the units available, but it seems like +20 whp is readily acheived.

Chi-Town has a good write-up about modding an SRT for high performance. Here's a quick breakdown of what he experienced:

A stock SRT6 has approx. 278 wheel horse power (whp)
Add a NeedWings Cold Air Intake ($500) and you get about 298 whp
Add ASP pulleys and remove your resonator ($1000 + $150)and you get about 344 whp
Add an InMotion ECU tune ($500) and you'll have about 348 whp - that translates to about 437 hp at the crank, which is a huge increase from the 350 that it came with.

That's about 70 whp for $2150. That's an 25% increase in power at only $31 per horse!

Check out Chi-Town's thread for more details:
https://www.crossfireforum.org/forum...ght=needswings