There’s probably a very simple solution to this involving a wire that has been disconnected during the transmission replacement, and not reconnected afterwards. You might find it’s a wire to a sensor that has been bumped or disconnected, and without this, the engine doesn’t know it is below operating temperature and, therefore, doesn’t richen the air-fuel mixture to compensate.

This compensation is how modern, electronically controlled vehicles make do without an old fashioned choke lever. But if the wiring isn’t connected and the sensors all working, the car doesn’t have the information it needs to run properly under all circumstances.

It’s a bit hard to imagine how removing and replacing a transmission could make an engine misfire or backfire. Unless, that is, you’ve managed to bump part of the engine’s electronic controllers, wiring, sensors or even something as simple as pinched or displaced a vacuum line somewhere in the engine bay. Incorrect ignition timing can make an engine do this, but, again, that’s nothing to do with the transmission.

It could even be a complete coincidence. But did the vehicle sit for any length of time while the transmission was being fixed? You might find the battery has discharged over time. Modern, electronically-controlled engines do not like low battery voltage and can run poorly as a result.

There are so few LDVs out there it’s hard to say how reliable they are, but we know the iMax and Carnival are good. I would go for the Carnival.