what is the difference between the two sentences?
I have always been
I always have been
There is no difference. They are both saying that the proposition “I have been able...” is true for all times T where T is at or before the present moment. The position of the “always” is mostly a matter of taste. In fact, while it would be rather archaic, and not particularly idiomatic, you could even get away with:
Always, I have been able...
I have been able always...
although the latter risks some ambiguity as to what the “always” pertains to. If I had occasion to use that form, I might throw in a comma for good measure:
I have been able, always, ...
Actually, go wild - you could even try:
I have been able ... always.
I have been able to roll my tongue for ages, since before I could walk even, in fact always, now I come to think about it, although I doubt back then I’d have known I was doing it.