Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
These types of problems can be very difficult to fix when they are so random in occurrence.... unfortunately the least expensive way to approach it if nothing noteworthy can be found via scan tool would be to see if the problem worsens to give more clues to what is going on.With that being said, three things come to mind with your symptoms that we see fairly frequently.
1) Intermittent coil malfunctions. We see these ignition coils fail in such a way that is not typical with an isolated cylinder misfire, but rather random misfires and lack of power etc then just suddenly coming back and operating normally. These are very tricky that way and can waste a lot of time trying to figure things out when they fail like this. If you have access to a known good coil, it is worth trying replacing the known good coil into one position on the engine at a time and seeing if any one location causes it to get better, indicating an issue with the removed coil.2) Wiring harness issues. It is common to see the wiring harness chaff on the back of the engine as it crosses over the transmission etc. Specifically the transmission dip stick tube is one bad spot as it has a metal bar sticking out for no reason that the harness straddles and eventually causes internal wiring damage. In addition the bundle as it bends around the valve cover is a weak area, and where it wraps around the AC accumulator as well. Basically, the whole passenger side main bundle there is problematic. One thing that is sometimes seen when this is the case is if you remove the fuse box cover you may hear clicking from it while the engine is running. This is a sign of wiring damage as well (a few of the wires common to fail will cause the ASD and fuel pump relays to freak out rather than staying engaged).
3) Lastly the PCMs are extremely trouble prone on these vehicles (and most Chrysler products of the era honestly). You can try having it updated to see if there is any improvement but usually replacement is in order. If it is updated at a Mitsubishi dealer and they are using the new MUT touch pad they need to use the old VCI with it... if they use the new VCI it will corrupt the PCM and make matters worse... just a heads up. Replacements I usually recommend getting a known good used one or sending it to a repair facility (like SOLO in south Florida, etc). New units from Chrysler (even through Mitsubishi) are terrible about arriving bad... the last one I had to do took 3 tries to get a good one, and when I contacted a Chrysler dealer about sourcing one through them they informed me they often take 4-5 tries too. They just aren't very reliable from Chrysler source, and a good used or having an existing one remanufactured would be preferred.