OK, I've also had a look at the Ginastera score, and I think your speed at the beginning, and at each of the a Tempo positions, is not too slow, it's more or less at the metronome speed 138 indicated. But of course you do slow down considerably when it gets difficult, for example in the passage beginning at bar 11.
It all sounds quite impressive, but when looking at the score there are some inaccuracies, mostly of rhythm.
The bar number references I give are based on counting the first complete bar as bar 1, and therefore the first 4 notes of the piece constitute bar 0.
In bar 4, the first note in the LH is one quaver (8th note) late, but the equivalent places in bars 44 and 66 are OK.
Bar 9 is a quasi 3/4 bar, but you are playing it as if it were a 9/8 bar, in other words you are playing this bar at 2/3 speed.
Bar 10: I think you are cutting this bar short by a quaver at the end because it sounds as though the separation between this chord and the first chord in bar 11 is the same as that between the two chords in in bar 11, but observe that there should be 3 rests between the first two and only two between the other two.
Overall in the section from bar 11, you are playing this as though the RH were just in 6/8 but time-shifted by two quavers relative to the actual bar-lines. You are accenting all the isolated short chords, and the first of every group of three identical short chords, and each of the long chords. The effect is to lose the sense of the music being written to be off-beat. Although I'm not familiar with this style, I suspect the intention is that the off-beat nature should be highlighted and become apparent to the listener (otherwise why would he write it like that?), and therefore accents should be placed as follows:
In each of bars 11 to 16, emphasize the first note in the LH, where the RH has a rest, because you need a downbeat reference.
In bars 11, 13, and 15, also emphasize the LH 4th notes where the RH has rests. Keep the RH chords light because they are not on the main beats.
In bars 12, 14, and 16, emphasize the 3rd of the A-B-D chords because it falls on the half bar. This should be stronger than the G-A-C chord.
In bar 17, emphasize the two A-B-D chords more than the other two.
Give similar treatment to bars 19 onwards.
In bars 35 and 37, you are playing the last chord as a crotchet (quarter note) instead of as a quaver (thus technically making these 7/8 bars). You get the rhythm right in bar 33, so copy it to bars 35 and 37. Again, I think emphasizing the basic 2-pulse of the 6/8 would help, e.g. in bar 35 emphasize the chords with the D on top, and then aim for the beginning of the next bar.
Bars 37 and 38 (and the last two chords of bar 36) seem to have E E E E F E D on top of the chords instead of the printed G G G G A G F (as though you were playing this bit in treble clef down an octave), this is probably what Eddy meant.
In bar 77 there is a Poco rit marked, but you seem to be starting the rit 2 bars early. I think the bar 75/76 echo of bars 73/74 should still be in strict tempo.
Finally, having observed the a Tempo marked in bar 79 (which is the 3rd last bar of the piece), should not bar 80 (which is all rest) also be in strict tempo? You seem to be holding this bar for approximately twice its length, before delivering the final note.