Having looked through the various responses to your problem as well as having a good look at the various pictures that you have posted - as someone who has some experience of growing avocado trees these are my thoughts as to what is going on with your avocado tree
As avocado trees are sensitive to sun due to the fact that their bark doesn't protect them and especially so when young and because of that - are best grown in a shady sport with bright light rather than a sunny one - until they are at least a couple of years old - I feel more than sure that the marking on your leaves - is sun scald.
As avocado tree roots are very sensitive and don't like having their roots disturbed at all and are known to suffer transplant shock - even if you been extremely careful not to disturb the roots and even more so if transplanted outside of the normal planting time - which is between March and June and as they generally have a tendency to look exactly as yours does at present - makes me think that is what the problem is with yours - transplant shock.
My apologies to
Chuck on this one - but I would strongly advise you NOT to use SuperThrive on your tree and especially not in its present condition - particularly as it is very strongly recommended that you don't fertilize an avocado tree for at least the first year - as fertilizing is best left until the tree is well established and even then only a yearly application of a light solution of a potassium and phosphorous rich fertilizer is all that is needed.
In order for your tree to start improving - I feel that giving it some shade is the greatest priority at present - as until it is in its more natural environment - instead of it recovering you are likely to see it getting weaker and weaker the longer it is exposed to the sunlight and if once you have given it some shade you wish to help it along a bit - as your tree can't take up water properly while it is in shock - you could try a light misting of the leaves every couple of days - as that often works wonders