Jeep cherokee fuel injector upgrades?
I don't know the mechanical aspects of your answer, but I do know that there are several upgrades that you can do to allow the 4.0 to try a little harder.
Less restrictive exhaust. Make sure your muffler is somewhat free flowing and the tailpipe is at least 2 1/4 inches.
Less restrictive inlet into the air box. The stock Air Filter itself is fine, however the opening into the air box is too small.
Run 93 Octane fuel and not Wal-Mart generic junk. Every 5,000 miles or so, add a 16 ounce bottle of SEA FOAM fuel treatment to the tank. It will keep the engine decarbonized and help it to perform at it's best.
My Jeep 4.0 has 260,000 miles since I purchased it new and has been trouble free!