Machamp, Rampardos are both bad match-ups for Tyranitar, and Hippowdon will be too, but there are some ways to improve your odds against all of them.
Basically you need to rely on Weaviles (pluralized because, especially against Rampardos, you will quickly lose your initial Weavile) to charge your Tyranitar to the point where it can OHKO anything. Machamp can drop the level X and OHKO you, but if your Tyranitar is fresh, Rampardos is going to need to drop 3 PlusPowers/Crobat Gs to do that, and Hippowdon is also. This means you have time to play Lucian's and move the energy off your badly damaged Tyranitar, drop a Moonlight, and retreat for a fresh one that you just charged with Lucian's, letting you get several consecutive OHKOs without giving up a prize. Rotom is another way to help you get another Tyranitar going if you do lose one that is fully charged (against these fighting decks, it will inevitably happen).
Dialga G is also not the best match-up in the world, although if you can charge Tyranitar up with Weavile (especially important here since Darkness Drive will be shut off) and attach an Unown G to prevent a possibly devastating Remove Lost, you should be able to at least give them a run for their money since everything they could possibly run will be in OHKO range; conveniently, OHKOs are Dialga G's biggest enemy. You also have the ability to tech in a Houndoom G, giving you a OHKO for 3 energy.
I think that the old Sableye/Felicity's-reliant Tyranitar is dangerous to run in this format and should be abandoned. You don't want to go first against a G deck or Machamp or Rampardos or Kingdra, you can't donk G decks, your Felicity's are useless for setting up Darkness Drive against Dialga G, etc.. Weavile is Tyranitar's saving grace in this format, and Lucian's will be as well.