I've been playing with the amerindians civs like The Incans and Mayans on Paragon and was quite enjoyable. However, a few things caught my attention.
The temple of kukulkan provides no benefit at all to the civilization. In higher difficulties, you will never build it in your harsh-land capital, more likely at danibaan (the mayan city that spawns on the stone) or elsewhere as this is a mega hammer-expensive wonder, thus providing you no rainforest benefit since the wonder provides bonus to rainforest tiles worked only by the city in which it was built. Even if somehow you manage to build it in your low production capital (considering higher difficulties the deadline is really short), only 2-3 tiles will give you the extra food, which is kinda lame.
Therefore, I would suggest changing the bonus to the whole empire rather than only in its city, similar to the moai statues that gives you +2 water improvement in every city. This would make this wonder somewhat useful to mayan 3rd uhv (helping you grow faster and developing your science) and even the incans. I can see some incan strategy involving in capturing chichen itza to give you the +1 food rainforest tiles and that way getting a bigger population to outgrow the European colonies in south America (cusco could grow a little bit more helping with the stability issue)
That could help to address these 2 civs 3rd uhv which currently can only be beaten through cheese in higher difficulties.
In addition to that, I also suggest adding +1 happiness to incan tamboos to allow you to become a bigger empire and have a higher chance to achieve the 3rd uhv (more than 90% of SA population)