So I'm playing Gnar Top vs Tahm Kench top, and he q pokes, and w pokes through the entire game. So fustrating, and he starts diving me when he has e and gets his 3 stacks every time because his passive slows. Can anyone tell me how to counter this? I know to rush Cleaver or Frozen mallet, but Tahm gets fed before I can even touch on a phage.
As some one who has played as and against 
top my tip would be to play some one with range farming and an escape and play safe early because he's one of the strongest early game duelists but falls of later compared to other tanks.
Cleaver and Frozen Mallet help to keep someone at a distance, and chase them down once you have a lead. If this isn't helping against a certain champion then it's the wrong thing to do.
I'm no expert at the matchup, but I'd say try Phage into BotRK with some early boots. Not really sure what to say about "Tahm gets fed before I can even touch on a phage", I guess start boots so you can get away from him early on? I've faced him a few times as Garen, though not recently, and didn't have much trouble until Tahm got an item or two, so maybe you're just being too aggressive and he is punishing you for that mistake.
If you wind up playing a tanky character, you can buy bramble vest. The grievous wounds will counter his E healing, making it safer to duel him. Also don't ever let him get 2 autos in a row off on you, because then he can chain Q into W to slow and eat you.
I love to build a executioners to tahm kench.
Tahm Kench has no counter pick your best bet is to survive laning phase. Hopefully, Riot will nerf him soon.
