My 1998 Isuzu Trooper's engine stopped working. Is there another American made engine that swaps out nicely?

Did you read any codes that are available ? what leads you to believe you should change the entire engine ? "Put Isuzu in Isuzu" because it will be a LOT LESS hassle. Call around and find an Auto Parts Recycler (junkyard) with a Hollander Interchange Manual. Tell them what you have and what you want to do and they would have the answer for you. Let say you decide to switch over to "American Ford, Chevy or Dodge power - you are looking at changing the engine (and if that doesn't have a retro-fit kit to mate it to), the transmission (and possibly shifter linkage reconstruction), then you could possibly modify (or completely replacing both drive shafts), the exhaust system to match the new manifold exhaust port locations from the catalytic converter forward (or possibly the entire exhaust if the pipe diameter is too small), the wiring for the "new" engine, the ECU (if so equipped), the radiator (if the old one has the connectors in the wrong locations for the new water pump, and to sum it up you would need to know if the "new" American powertrain had enough room in the Isuzu for the "spread out" of accessories (A/C, power steering, Air pump for emissions, Alternator) connected to the belt (serpentine) or belts. I would recommend you just put in another Isusz engine and save the hassle.