Fitness is an issue among some the local players partly because of climate, partly because of lack of professionalism. Players who play in hot countries cannot train and play at the same level as players from moderate climates...that is one of the reasons why the game is faster in Europe. Foreign based sometimes look unfit because they are jetlagged, or not playing enough for their clubs or cannot take the heat. But I think the general fitness level with the fellas is good now. We didn't look unfit playing with 10 men against the US to me.
The biggest diference between TnT and countries like the US/Mexico is the size of the population. If we were larger we would have 10 Stern Johns, 5 Latapys, 15 Birchalls, 4 Shakas...etc. That improves your talent pool, and the local league would be much more competitive, more players would gain international club exposure etc...
2nd...technical ability. we can do the basics well, but we sometimes need to play at a faster rate in the attack. Greater confidence in technique (as well as fitness as you mentioned) helps with a crisper, faster, more efficient, more disciplined game. But in the end, technique and fitness would not be an issue if we were sufficiently large. It would be cake to find 22 very fit, technically gifted men if TnT had over 200 million people living here, especially with football being such a big sport here.