Nostalrius Begins - Quality wow vanilla realm (1.12)

i noticed it when i was around 18-20 that the rogue i was leveling with was getting more XP for kills than me...he was 2-3 levels ahead and we were killing things my level maybe a little lower...he was in his 43 and i was 39 and he was getting 16-20 XP more than me for the mobs we were killing witch were 39-41... now i am 48 and he is 54. he still gets more XP than me when we kill mobs my level. i feel this is the reason the separation between me n him has happened for we level together and play at the same times.
please if i could receive some help from a person who is apart of the server...i feel like iv been cheated cause the amount of XP i receive killing mobs my level are substantially lower than what others get doing the equal