Agreed - shorties will do very little for you.
HOWEVER, long tube headers provide their own challenges, namely installation and cost. I'm not aware of a setup that is bolt-on...so it typically involves some custom pipe bending, welding, new cats and a longer and knuckle bruising install time.
You will also need to purchase a new exhaust system, so the overall cost is going to be quite high. To fully benefit from your new found flowing exhaust, you should also switch to a performance air intake and have your computer programmed.
If you simply change up your exhaust system w/o modding the air coming in and the computer, the benefits will not live up to the chuck of change you just dropped.
Your rig weighs 6700lbs, so performance enhancements are always relative
There are guys on here with a lot more experience then me that may counter, so this is just my $.02.