It had high NOX readings. I bought a new O2 sensor and a Flowmaster catalytic convertor, which did the trick and the Jeep passed emissions. The downside is that there is extreme pressure pushing oil out of the dipstick tube and I had to purchase another catalytic convertor last year. I realize I must perform a leakdown test to see what exactly is going on inside the engine. Would it be more cost effective to rebuild it than swap it out? It’s only got 149,000 miles. I do plan on keeping the Jeep, upgrading the axles, and putting on a 2 1/2-inch Skyjacker lift kit. My other plan is to upgrade to a Ford 5.0L truck engine and get an AX-15 transmission. What is the best bang for the buck option? It already has a Gale Banks header and an Airaid intake. The Jeep is a blast to drive on- and off-road, and with the 4.10:1 ratio axle gears it moves out nicely!Sean Jennings Via email Except in extremely rare cases, an engine rebuild or a remanufactured crate engine will always be more cost effective than an engine swap. Engine swaps have many costs and complexities that are often overlooked. These costs add up quickly and include things like the wiring, adapters, engine mounts, radiator, ex...