This is the last comment I will make on the issue of the team. I explicitly state I am not taking credit for the combination. Any person who plays DPP knows all stall looks similar. It's not just Earthworm who has used a team just like this. It's VIL, imperfectluck, stvn, Taylor, and so on. The one I credited is august since he got me going with this. Finally, I have provided many of the lessons I use in Battling 101 in this RMT to help people use this. This is how I stall in DP. Therefore, it is Kevin Garrett Stall. You don't have to like it, but you do have to respect the time and effort I put into this. It's the presentation and how much people will absorb from it that I care about.While this is a good team and while I'm sure you've put a lot of thought into it, this team is literally Pokemon for Pokemon, move for move Earthworm's stall team with Scarf Tyranitar over Heatran. It seems a bit arrogant calling it "Kevin Garrett stall" when 5/6 Pokemon are carbon copies.
You seem terribly weak to Breloom. While you can certainly force it out with Roar you lack many ways to significantly harm it. Three of your Pokemon can't break its Subs at all while Tyranitar is wrecked unless he can come in with its Sub down, and even then Superpower will only do around 65% to 12 HP Breloom. Blissey clearly isn't going to combat it well and Breloom is always 3HKOed which can easily turn to a 2HKO with Stealth Rocks and ~10% of prior damage. Since most of your team can't break its Sub it doesn't need even Spore to cripple you.
I highly reccomend you run Specially Defensive Heatran in the last slot as it gives you an extra way of killing Breloom but also an extra Dragon resist. Something like mixed Dragonite will run your team to the ground as your current Steel resist has no Wish support and can be worn down. It can easily Roost off SR damage and hits from anything here except for Tyranitar who, as with Forretress, lacks Wish support. Heatran probably won't solve that, but it might help.
Good luck!
I would not say I am terribly weak to Breloom. Breloom on its own is not a big problem at all. However, when Breloom is coupled with a few Pokemon that can make holes in this team, it is hard to play against. That can be said for almost any team with a certain threat. We're playing DPP here. Team matchups don't determine everything, but it's when certain combinations of things make it too big of a deficit to overcome do you lose. I will probably try Heatran and a few of the other sixth slot Pokemon that people have suggested.