No, that's a really cool concept, I like it. We can definitely work with that, I think. If he's had a lot of Githyanki cultural influence, his favoured class would emulate their own - which is Psychic Warrior, as far as I'm concerned. I'm using the Githyanki from the XPHB, and by the book their favoured class is either fighter (for a low psionic campaign) or psion (for a high psionic campaign). Fighter makes sense, but I don't like the variant of psion. After all, they live in a very militant society, and it's my view that they'd be much more driven to the Psychic Warrior class.
So, Pyshic Warrior is something to think about. It could be made to work with the wanderer concept (I would have no problem swapping round some class skills to give you Survival and anything else you feel is more appropriate to your concept), and if you wanted to work the healer thing in there you could consider powers like Body Adjustment and Empathic Transfer. It might not be the most efficient way to make a healer, but it's pretty flavourful and cool. Of course, I'm assuming you have the XPHB. If you don't then I guess all that's pretty much a moot point.
So, failing that... with a few additions of bits of flavour to the concept that don't seem to be there already, you could perhaps go for a Druid. The Githyanki have no Druidic tradition I'm aware of, but if you left them early and had the right experiences early in your career I wouldn't be averse to you taking a single class druid (though it would be more realistic I suppose to make you take a few levels of fighter or something similar first to represent the time before you were converted).
A Cleric could work too, if you like. I wouldn't worry too much about the Planar Cleric variant in the Planar Handbook - the definition of a Planar Cleric, as far as I'm concerned, is simply a cleric, on the planes. A lot of different powers could possibly make sense for you to worship, so... whatever you fancy I guess.
Alternatively, you could if you wanted to go with your original ranger idea. Put the focus on combat, wilderness skills, and more of a wanderer/loner concept, as you say, than an explorer, and there really wouldn't be too much overlap with Synchronicity - I think I perhaps misunderstood your intial intentions, if this was what you were wanting to do all along. In which case I apologise.
Or you could, as you said, adapt that idea to a barbarian, which might be quite a nice twist on it.
So... yeah. Any of the above work fine, or any of my earlier Savage Species ideas if you come round to them. Use whichever you want, and tweak it around as much as you like. I'm really quite accomodating when you get to know me, I promise!
On the upside, it looks like it's all sorted now, so I can just fade into the background. 
I decided to try my luck with the dice roller, and the 
