I know both of the Rambam and Ramban listed all 613 mitzvos, and they differ in some (I think like 16ish?)
What are the ones upon which they differ? If possible please include why they differ in specific instances.
The list of differences can be found in an appendix to the Minchas Chinuch.
Ramban includes all of these positive mitzvos, which the Rambam doesn't
Mitzvah 1: Positive mitzvah of eating maaser sheni.
Mitzvah 2: Positive mitzvah of not eating impure trumah
Mitzvah 3: Positive mitzvah of not selling shvi'is fruits
Mitzvah 4: Positive mitzvah of settling Eretz Yisrael
Mitzvah 5: Positive mitzvah of leaving a way for the enemy to retreat
Mitzvah 6: Positive mitzvah to eat fruit trees when sieging a city
Mitzvah 7: Positive mitzvah to remember Miriam verbally
Mitzvah 8: Positive mitzvah to be wholesome with G-d
Mitzvah 9: Positive mitzvah to separate trumah from the best
Mitzvah 10: Positive mitzvah for every korban to be one of the three valid species
Mitzvah 11: Positive mitzvah to offer all korbanos between the two temidin
Mitzvah 12: Positive (?) mitzvah for the Pesach not to be eaten by day
Mitzvah 13: Positive mitzvah to kill a killer
Mitzvah 14: Positive mitzvah not to benefit from clothing or a house with tzara'as
Mitzvah 15: Positive mitzvah to thank G-d
Mitzvah 16: Positive mitzvah to keep your brother alive
Mitzvah 17: Positive mitzvah to return interest
Ramban includes all of these negative mitzvos, which the Rambam doesn't
Mitzvah 1: Negative mitzvah not to forget belief in G-d
Mitzvah 2: Negative mitzvah not to forget the standing at Har Sinai
Mitzvah 3: Ngeative mitzvah not to misplace vessels in the beis hamikdash
Mitzvah 4: Negative mitzvah not to slaughter kodshim intending to eat them
Mitzvah 5: Negative mitzvah not to eat kodshim outside of their place
Mitzvah 6: Negative mitzvah not to eat the bird slaughtered for a metzora
Mitzvah 7: Negative mitzvah for levi'im not to take trumah
Mitzvah 8: Negative mitzvah not to accept shekalim from non-Jews for the purpose of korbanos tzibur
It is important to note that the Rambam and Ramban agree with each other most of the time that these are obligations, but they disagree about whether they are de'oraisa.