not sure about your 4.0L, but I just got one for my 2.3L/manual and the gain is amazing! I got a 87 performance, 93 performance and a 93 torque tune. I have a k/n fipk intake and gibson exhaust and when I tried the 87 performance tune, I noticed a slight differance, with the 93 performance tune I noticed a HUGE differance, with the 93 torque tune I really couldn't tell a differance between it and the 87 performance. I am getting rid of the 93 torque tune and replacing it with a 89 performance tune so I can give it a try. The increase in power that I got with the 93 performance tune is a ton more than I ever could have expected. Everyone's vehicle is different depending on the engine/mods, but I highly recommend the Bama-Tuner.
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.