A turbo is just going to help out a little bit on the highway. You dont have to boost much to get some good power out. It isnt always to go fast. Just to help out getting to some trails that arent too close to home.
There is a tubo kit out there I read an article in I think JP magazine about it. If I remember correctly they had some good things to say about it. They liked the turbo over a supercharger because it didnt effect crawling on the trails but gave you that extra kick to get going on the highway. Do a search and you should find it.
Bell Engineering used to make a 4.0L turbo kit, but I don't think it's still available. You might want to contact them for advice.
A low-pressure turbo (8 psi or so) is perfect for an off-road truck, because properly set up, it will give you gobs of torque from right off the line. Such a system could easily add ~100 hp and ~150 lb-ft of torque to a 4.0L, with the peak of the torque curve somewhere in the area of 1800-2000 RPM.
Now, if I could just find a nice turbo kit for the 2.5L...
Michael Amper, HV-K2TIV & ZA-WPWN327
1998 Jeep Wrangler SE
If you're looking for a turbo, try 505 Performance. They have a turbo kit for the 4.0liter, but the drawbacks seem to far exceed the positive aspects.
2005 Black 'Con. The goods:37"SSR's-15x10 M/T's-RE LA 5.5"w/ 7.5"springs-JKS 1.25"BL-M.O.R.E. 1"MML-Alloy 5.13 gears-PSC HD steering-PSC rockrings F/R-PSC rockers w/ slider bars-OMF rock domes-Pro Fit VSM-Hanson 52" rubicon bumper-JKS BPE's-Power windows-Husky liners-Alloy tube seals-AEM intake-Poweraid TBS-Banks header and cat back w/ monster muffler-empty pockets.
-OlllllllO- Life is Good
talk to jason at redrock4x4, he got the 505 turbo on his jeep
2005 Unlimited Rubicon Hard N Soft Tops, Clayton Long Arm on RE Coils, Warn Bumper/Tire Carrier, Warn Winch N Bumper, Currie Steering, JKS Quicker Disconnects, JKS Front Trac Bar, Bilsteins, CO2 System..Yada Yada Yada
If you wanted to do a custom turbo setup the hardest part would fuel managment, it would take a lot of time and custom fab work, probley make your own mani,charge piping etc, check out homemadeturbo.com and do a search, you could probley use a Grand National or old T-bird turbo would be a good size, would cost around 1000+ i would think