V8 hands-down. As a bonus you'll also be getting a kickass tranny in place of a crappy one and a decent rearend in place of a crappy one. There's nothing wrong with the 4.0 itself, but Grands are just too heavy for them.
The blend door problem was also addressed in '04.
Did I mention you should get the V8?
So I installed the flux capacitor but the Jeep just won't do 88 mph.
-'99 WJ Limited, 4.7, Patriot Blue, 2" BB, 31" Mall-Terrains, Pavement Princess
-'97 TJ, Stone White, 4" Superlift, 33" SSRs, lunchboxed rear, 12K Titan winch, and 2.5 litres of exhillirating performance.