How long since a tune-up? Any applicable trouble codes? I realize with cross-over years, with some makes and models, for me, mostly GM, Accessing trouble codes can be a pain.
If the engine will race when it is slowing down, might be a tranny issue? Otherwise I look somewhere else. Have you ever changed the fuel filter? Use a gage and check fuel pressure. You may have to check when problem is ongoing. Don't take any fuel lines loose, unless your sure there is no pressure on the system.