I have no idea what they're like live nowadays, though I haven't heard anything about them going sour. Maybe check out one of their more recent live albums. They haven't released one in some time now, since about 2004 or so, but it'd give you more idea, I guess.
The band really mellowed out after Duane died... Eat a Peach and Brothers and Sisters, the 1st couple of albums without him, don't have that hard-edged blues sound. There's a little bit of a country western tinge to them, but still good though. I love "Blue Sky", "Jessica" and "Southbound".
To me, Idlewild South doesn't have it half as much as their debut either though. The style of those two albums is really quite different. It's like on their first, they just thrashed out a heavy blues set, but on Idlewild, they stopped to try and more accurately represent the full spectrum of their sound, with the lighter and the jazzier moments too.
Eat a Peach is, as I felt it might be, a mixed bag, though not in terms of quality. Basically, everything on here is great, but because the album is so obviously made up of three uneven thirds, there's no unity at all. The post-Duane songs are all great, but at, what, seventeen minutes, too brief before the new Fillmore tracks kick in. I'm still uneasy about there being forty minutes of live material in the middle of an album, as great as it all is. And the Duane-era songs are very good, but embedded in the midst of a strong studio album, they'd really feel like they'd been given justice. Here, as ten minutes of studio material after forty minutes of live material, they just sound tagged on the end, like an afterthought. Putting the first and third of the three parts together helps a little, but it still doesn't feel like a complete album. But to be honest, I think the band just had to get this material out of their system, and it's all good stuff, so it works, I guess.
Brothers and Sisters is, like the first two albums, another really strong album. The only track on here I'm not totally sold on is Come and Go Blues. The rest is solid. It's a real pity the band didn't keep up the momentum.