JBA makes a shorty style header for our trucks (only ones I know of)....but on a stock 4.0 - it's not worth the money.
I have them (More Info
) and I would say that it doesn't do much by itself.
However, now that I'm supercharged - it doesn't hurt anything. lol
Back before the supercharger I even had all of the "supporting mods" like a Magnaflow SS Cat-Back Exhaust, K&N intake, as well as the SCT XCalibrator-3 tuner tweaked for the headers...but didn't see anything directly when I added the headers to the combo.
I also have the titanium ceramic coated headers from JBA. Of the available finishes JBA offers, this version has the "highest thermal & corrosion resistance level" but you pay for it (about $150 more
than the basic stainless steel setup from JBA).
The following is a list from lowest level of thermal protection & corrosion resistance to the highest level (Info found here:http://www.jbaheaders.com/details/headerfinishes.jpg
Nickel-Chrome Plated Mild Steel = "Mild Street"
409 Stainless Steel = "Mild to Severe Duty"
Silver Ceramic Coating = "Mild to Severe Duty"
Titanium Ceramic Coating = "Extreme Duty"
To be honest I didn't notice any real gains (especially not for all that $$$).
Even before I put them on...I found most people here said in general, not to expect a huge difference on the 4.0. I would agree with that statement.