My van has been hesitating and back firing.

We need to get the fuel pressure reading and check for codes in the pcm. If there is a misfire, somtimes it will not be detected unless we perform a cylinder balance test. There is probably a rev limiter/cutoff built into the pcm that shuts down cylinders so not to damage the motor when revved in park. Backfireing could be a fuel starved engine, or cylinders not firing in the correct order. I will need some more information to guide you further.