I have to agree with PlatinumDude. Arcanine will be a better choice than Houndoom in your case. Besides dealing a great deal more damage to Chansey, the overage provided by Arcanine is superior. Plus, you get the priority of Extreme Speed, and if you felt so inclined, you could run Crunch to help counter the mess of Psychic types in UU.
All that considered, I think Lapras is highly out of place on this team. Lapras is pretty much lost on any team that doesn't run Rain. I want to run Suicune by you for a moment. Yes, it is a Special Sweeper, but it has twice the use usefulness as Lapras and would only benefit your team accordingly. I'm going to suggest an offensive Calm Mind set.
Suicune @ Leftovers / Life Orb
252 Special Attack / 4 Special Defense / 252 Speed
Timid [+Speed; -Attack]
- Calm Mind
- Surf / Hydro Pump
- Ice Beam
- Hidden Power [Electric / Fire]
Lastly, I'm having second thoughts about Miltank and Sceptile. You just have some better options out there to choose from. I'm going to suggest Aerodactyl as a new Lead, and Heracross as a new Physical Sweeper.
Aerodactyl @ Focus Sash
248 HP / 136 Defense / 124 Speed
Jolly [+Speed; -Special Attack]
- Stealth Rock
- Rock Slide / Stone Edge
- Taunt / Roost
Well, you're not going to be healing your team of any statuses, but you will be outspeeding most of anything you'll encounter in UU. Aerodactyl's Speed rivals that of Weavile, Jolteon, Crobat, and Azelf, so it's safe to say that it already outclasses Miltank in that facet. Despite what Aerodactyl was originally known for, this generation allows it to play a little more defensive role having typing gives you some useful resistances. Stealth Rock is just Stealth Rock, lay those with ease. The first move is more of less a toss up. You have the choice of Rock Slide (more PP and accuracy) or Stone Edge (less PP, less accurate but more powerful with a high critical rate). Personally, I like Rock Slide. But Stone Edge can be useful if you don't really plan on using Aerodactyl for long. Earthquake is to hit Poison and Steel types, but I have heard of people running Toxic > Earthquake in Stall teams. Finally, and this is the hard part, you have the choice of Taunt and Roost. Let me give you the pros and cons so you can make an educated decision. Taunt is crucial to Aerodactyl, saving it from the slew of status attacks and set-ups. Roost will give you reliable recovery. And since Aerodactly has the Speed to pull it off well, you'll be able to heal off those Ice, Electric, and Rock type moves with relative ease.
Now, to replace Sceptile, I was thinking something like Heracross who actually breaks through RU and sits comfortably in UU. This is completely up to you. You mentioned that most of your Pokemon are RU so I'm trying to give you some more UU options. Houndoom isn't the Pokemonto justify an entire tier shift, but high profile Pokemon (some who were very recently bumped down from OU) is very much worth it, in my opinion. Heracross will also be another strong Physical attacker, so you'll have more security against Chansey and the likes. I'm going to suggest a Choice Scarf set. If you don't know what a Choice Scarf is or what it does, please look here.
Heracross @ Choice Scarf
4 HP / 252 Attack / 252 Speed
Adamant [+Attack; -Special Attack]
- Close Combat
- Stone Edge
Yes another self explanatory set. This is all out offense. With a base Attack stat of 125 and two very powerful STAB attacks, Heracross makes a prime client for a Choice Scarf. Best of all, with Heracross' ability Guts, it performs outstandingly as a Status absorber. While Miltank would be healing your team of statuses, Heracross can switch in on them (with a bit of prediction) and punish your opponent for even considering inflicting your Pokemon, boosting Heracross' attack stat. This is only made sweeter by the Choice Scarf, making the two a lethal combination. With Close Combat and Megahorn, which have surprisingly good synergy, you'll be able to hit a fair majority of the UU tier with crippling STABs. When adding Stone Edge to the mix, you're literally able to hit everything for at least neutral damage. The last move slot is reserved for Pursuit (or Night Slash, but I like Pursuit more) so you're able to pseudo-trap opponents and hit them for super effective damage. I feel obligated to say though, if you go with Night Slash, you'll be 2HKOing even the bulkiest of Jellicent. Which is quite an achievement that not all Pokemon can claim. Simply put, it's a coverage move, but worthwhile on any Choice Heracross set.
I'd also like to mention quickly, you have a lot of options with your Pokemon here. But, with the chances made (Aerodactyl > Miltank; Arcanine > Houndoom; Cresselia/Alakazam > Musharna; Heracross > Sceptile; and Suicune > Lapras) you're actually fixing a lot of the typing weaknesses I mentioned in my last post. The only thing I'm still worried about are the Dragons, but your Fighting Type weakness is all but dissolved. These choices are all up to you though. I'd like to see more powerful UU Pokemon on your team so you fair a better chance in that tier's environment. Hence, the changes I've recommended. However, you have many, many other Pokemon to choose from. I suggest you read up a bit more on solid UU Pokemon and weigh the pros and cons. You have the ingredients for a good team here. I look forward to you posting a tested and proven team here. :)
If you have any other questions / ideas please let the raters know and we will be happy to help!