Hello I Have a 1990 dodge Grand Cavavan LE 3.3L and I've started having issues with it shutting off in reverse, its not the IAC valve, that has been tested and it works fine. I can turn it on in Neutral and put it in drive and it works fine but when I'm going to park as I'm shifting into reverse in turns off, if i don't completely turn of the ignition it won't turn on again. i don't know what to start with, also the back up light don't turn on the PRND switch is new and the neutral safety switch is brand new the fuse is fine and the back up light bulbs are new as well and the shift solenoid pack isn't new i got it from the junk yard cause the old one was not working properly. so I'm trying to figure out what it is cuz i can't even keep the van on even if i accelerate a bit so i got push it

 

You must have a wire grounding when you put the engine in reverse. Check all of your wire harnesses for shorting to ground.