Q: doesn't move when i put it in reverse but then i put it in 4 low then reverse and it slips but it moves.

You have the Chrysler 46RE transmission. Among the possible causes of what you describe is a rear servo piston that is sticking or broken, pin bore wear and/or the reverse band is slipping. The servo piston on the 46RE has a tendency to get misaligned in the bore and that results in inadequate force on the band. If bad enough, reverse line pressure will apply force against the misaligned piston, breaking or damaging the piston. The bore can also get worn resulting in band apply pressure that is too low. I would consider the foregoing possibility first. This can potentially be repaired with the transmission still in place but if the bore is damaged, that could be a problem because the bore is integral to the case. If you want this investigated, and repaired if possible, please request a no reverse diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.