@KentB while I'm not a fan of the infinity personally, mainly because of the crazy cost.
It sounds like you very much had the straps WAY too tight. There should be no restriction in the water. The straps should be loose enough to get a full fist underneath them. The crotch and waist strap do all of the "holding" the shoulder straps are there for extra support when you roll over and to allow you to carry it around on land. Think of it more like a hiking backpack for when you're in the water and you want all of the support to come from the waist.
Coming from the X-wing I wouldn't expect you to see many improvements in the water as far as trim goes because the wing on that works basically the same as in a bp/w so you shouldn't notice much of a difference there. On land you will probably notice some comfort differences due to the lack of thick shoulder pads, but it should be much less restricting in the water if sized properly.
You should be using the bottom dump on your wing to dump gas with the exception of the first ~10ft of descent and last 10ft of ascent, but if you like the pull dump, you can probably swap it over. I think they're the same threads on Tusa's bcd's.
That said, it is certainly a learning curve and dive 1 with it improperly fit isn't going to give you a good basis on what you should be experiencing. Try to get the shoulder straps nice and loose and then report back