1. Yuusuke's path to redemption goes much further in the manga! He not only helps Kuwabara pass his test, but helps a little girl who died find peace and stop haunting her family (This is the character of Sayaka, actually!) and helps a tanuki transform into a little boy for a grieving old grandfather. From what I remember, Togashi had stated these small and comedic scenarios without much fighting were what he originally had in mind for the series as a supernatural mystery manga.
2.The character of Jorge is not featured in the manga, and is an anime exclusive. He was originally interchangable with other oni in the Reikai, but one was eventually settled on for comedic bits and exposition dumps with Koenma.
3. Kurama's human backstory is elaborated on further when he explains to Yuusuke why he must save his mother. As a young kid, Kurama reached for a plate on a high shelf only for them to come tumbling down. His mother shielded him, but cut her hands on shattered glass in the process. Kurama believes this to be the point in his life when he realized the altruism of human beings, and truly loved his mother instead of seeing her as a means to an end. This scene is shown in passing at the end of the series when Kurama is working for Yomi, but the full context is never included. Pretty important scene if you ask me!
4. Following the defeat of Suzaku and the other Saint Beasts, Yuusuke and Kuwabara return to school in an absolutely exhausted state. They learn from Kuwabara's friends that two dopplegangers have been terrorizing the student body, and blaming it on the Spirit Detective and his rival. Kurama and Hiei watch it from afar, with Kurama still not fully healed. They discuss how Hiei needs to keep serving the Reikai for his freedom, much to his chagrin. Anyways, it all culminates in a huge fight between Yuusuke's friends and the dopplegangers, who ended up being some incredibly weak demons doing it for show. The chapter ends with Hiei giving Yuusuke the tape explaining his next mission, just like in the anime.
5. An absolutely massive ommission in the Dark Tournament arc is that Yuusuke's mother is present at the stadium alongside Shizuru, Botan, Yukina, and Keiko. She's seen once or twice before the girls arrive in the anime, but acts as another supporting lady in the cast throughout the manga. Maybe she forgot to come over in the anime?