I highly recommend the x cal 2 tuner. I only have a 2.3L/manual trans., but the results are more than I ever could have expected. I picked the 87 performance, 93 performance and the 93 torque tunes. The torque tune didn't seem like it did much, but with the 4.0L I have seen a few people post that it works very well. Same with the shifting firmness. Another good thing about the Bama-Tuner is that once you get it and try all the tunes out and you find one you don't really care for, they can email you whatever other tune you may like to try. It took me a few minutes to figure out how to get the tune file from my email to the unit, but now that I have done it once, it's very easy. You can take a tune file from your email, transfer it to the tuner and have it in your truck in less than 5 minutes.
HAD A 2003 2.3L, amsoil duel remote by-pass filters, amsoil pre-oiler, all amsoil lubricants in everything, gibson sidswept exhaust, hurst shifter, K/N fipk intake, roush front and rear sway bar kit, frozen rotors, hawk performance brake pads, flex-a-lite electric fan(FLX-180), bilstein shocks, suvlights headlight harness, piaa extreme white headlights, optima redtop, ta performance aluminum rear end girdle, limited slip rear carrier, stainless braided brakelines, bama tuner.