I made a lot of Gliscor decks since the spoilers came out, this one has almost the same techs as most of my decks. I had 3-2-2 Gliscor line and tested with Breloom (+ Moonlight Stadium) or Donphan, because only one attacker isn't very much.
I don't really like Gyarados here because of its retreat costs. One Shuckle should be in fix - it's just too useful to leave it out because many good players run Call Energy.
The deck may do well against Kingdra and AMU, but it has huge problems with Eeveelutions & Togechomp (especially your Gyarados version, Leafeon has resistance and Garchomp OHKOs with PlusPower) and absolute autoloss to Empoleon decks with Dawn Stadium.
To fix those matchups, I lately made a list with stage 2 lines - Jumpluff for stalling and 1-0-1 Bastiodon tech. Didn't test it yet, but I think its too inconsistent and too flippy.
Maybe you could even try a larger Bastiodon line to take damage with 4 special metal energy and do 60/40 after that. But retreat costs are still a problem here.