Hi tglp,
I've only played/recorded the Barcarolle No. 6, but I've heard No. 4 so can probably make some general comments as I have the score here.
This piece rhythmically is a sicilienne, a peasant dance form that is graceful, slow, soothing and pastoral in character. So that character is what you want to portray throughout. The tempo is allegretto, so yes, it is a bit slow at the moment, but only play within the limits of your capability. If you force speed, it'll invite more errors. A way to get it a little faster is to turn on the metronome and move it up from your current speed just two notches at a time at the most. See if you can then play through the piece with the metronome. (The end-game is not to play in a metronomic way, of course, only to see if you can keep up the speed without getting into trouble.) Depending on your success or failure, move it up again one or two notches, or move it back a notch for another trial. Once you find your new plateau, put the metronome away, as you already have that pulse in your head. Only go as high with the metronome as you are comfortable while maintaining complete control--no faster.
Give even more attention to the balancing of the hands. There are times that the melody is in the right hand, but also occasions with it shifts to the left hand. Wherever the melody resides, make sure it is etched clearly in the foreground. The other hand doing accompaniment is merely background, so tone it down. The trick here is not to attempt to amplify the foreground hand to drown out the background hand. It'll just increase competition between the hands such that both get louder! Instead, lower the volume of the background hand, and then the melody will soar like magic on its own. Thus, think of the solution in reverse rather than in terms of what seems obvious.
Bear in mind at all times that Faure is a Late Romantic composer. There are times that he expects some very effective romantic surges in the playing. For example, on page 2 starting at the cresc. in the second line, working up to the f in the third line, but really culminating in that wonderful B flat tonality in the first measure of the fourth line--all of that has to be a very calculated and effectively executed big romantic surge. Think like Rachmaninoff there. You find that again over on page 6 before the coda.
On page 2, top line, third measure and elsewhere in the piece, note the tenuto markings over the melodic notes playing a partial scale. The ascending/descending chromatic scales underneath those notes is accompaniment within the same hand as the melody. So the underlying scale is more deemphasized. That means you have a layering of sound: The tenuto notes are loudest, the underlying scales are quieter, and the LH accompaniment is still quieter. Tenuto has an obvious meaning which is to hold those notes for full value while the underlying figuration is played. But there is a hidden meaning too. To ensure that those notes are sustained and heard for their expected durations, you need to impart a bit of accent to ensure their success. The idea is to prevent premature tone decay.
On page 3 top line, make sure you're voicing the tops of the RH octaves' scale. Note that you have a contrary scale in the LH, also of interest to the listener. I'd consider that passage to be a duet and would enable both hands to be equally balanced there as you do the crescendo. On page 3, on line 4 at the cantabile (playing in a singing style), play the RH leggiero--lightly, lightly so that the LH melody can dominate.
Bottom of page 4, the LH is so much in charge there that Faure even indicated rinforzando accents. So don't be bashful in the execution, BUT notice the entrance of the diminuendo and rallentando and execute them accordingly.
Page 4 last measure and page 6 line 2 last measure and line 3 first three measures, you have dots under the legato slur marks indicating portato touch there. To me your portato sounds more like staccato. Portato is more of a weighty, pressing touch using relaxed arm weight rather than staccato's detached sound. Be sure to differentiate the portato touch.
Coda: Be sure in measures two and three for the rolled chords that you voice the bottom notes forming the partial descending scale there.
I think you've got the basics of this piece pretty well in order. What you mostly want to focus on now is the musicality or the expressiveness of the music. Do slow practice, everything at forte to assure proper articulation. If you have breakdowns, do four or five slow repetitions, waiting a few seconds before each repetition, to fix them. Then leave that and turn to making music, attending to phrasing, voice leading, expression, dynamics, nuances, etc. Again, try to increase the tempo, but only within your level of confidence and limit of capability. One of the hallmarks of Faure is is ever shifting centers of tonality. As a result he has accidentals everywhere, and the pianist has the nightmare of keeping them all straight. You've done well with that!
You've still got practice time before your performance. Make the most of it by practicing intelligently and efficiently, all the while having your ears on high alert listening to every note you play to ensure that each one is conforming to your musical intent in playing your interpretation of the piece. This is the polishing phase. You're almost there.

I hope this is helpful.