Try wearing the trisuit for just a little bit before race day and swim around in it so you get comfortable. If its skin tight then it shouldn't slow you down rather it would help you out. If it isn't skin tight and then there will be drag which could potentially slow you down. To help with shoulder pain make sure you stretch out your whole shoulder area starting across the chest then down on your tricep with your elbow up above your head. Makes sure you shake your arms out so they aren't too tight if you're swimming afterward. Last tidbit of advice, a well guarded swimmers secret(feel free to tell everyone haha) rub your back and shoulders and pecs with Tiger Balm(not for sensitive skin) or Icyhot literally minutes before the race. Trust me this makes a huge difference. The ointment will loosen out your muscles preventing shard tight pains throughout the swim. Tiger Balm for those of you who don't know is Icyhot on steroids and is not to be treated lightly. This stuff burns so if you have never done therapy like this go with the Icyhot(both can be found at a local drug store). Also, the water will "enhance" the Icyhot's effect so be prepared when you jump in for it to burn slightly more. That is what I always did religiously before every single race(not triathlons though, I would check to make sure its legal though I don't see why it wouldn't be) and it really helped prevent mid-race pains and knots. Again I hope this helps! Keep us posted and let us know how you do!