The timing on a 4.0 is set,it cannot be changed,once it is set it will not change unless the dist is removed and replaced incorrectly.
You may have other issues like fuel pump,plugged filter or restricted exhaust.
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89 xj in progress D44,4"x 2" lift
72 Restored chevy truck 4x4,lockers,built 350,approx 400 hp.