What codes are you getting now? Is the $$$ light on? Runs rough how (explain)? Is it idling ok?
For misfires, usual suspects are plugs, coils, vacuum leak, not enough compression, timing, plugged CAT’s, etc. I think yours may also fall on a TSB for a throttle body assembly for a rough idle.
I guess we need a better picture of what going on with your Expy.
Could it be turbos? Kinda hard to believe, but possible. I am driving turbo’d cars and trucks for a long time and never had a single turbo fail yet and they were way past 200k miles. Unless you skimped on the oil changes.