My 88 is a trail only xj. 4.0 auto trans 4x4. 8.25 rear with d30 front. 3.55 stock gears. When I pull up to even a small 1 ft tall ledge and try to ease up it, it is gut less. What would yall recommend checking for power loss? It's got new plugs, wires, etc.

 

Your first step may be a compression test of all cylinders. Are you blowing any smoke when it strains?