I remember being very impressed watching Roddick beat Berdych at Wimbledon in the 4th round in 2009. The match was even more one sided than the scoreline suggested, as he completely toyed with Berdych, employing a lot of variety, especially with the paces and spins off his shots and his volleying, slicing well and never looking remotely troubled at all on his serve (he didn't face a single break point). That was a match in which he displayed an effective combination of showcasing his strengths from the earlier stages of his career, alongside newly improved features of his game under Stefanki.
Sections of the British media acted as if a Federer-Murray final was a foregone conclusion at that tournament, and were even 'previewing' how that 'dream' final would play out, ahead of the semi-finals. Surely a further motivating tool for Roddick there.
In terms of the split with Gilbert, I remember reading that he clashed with Roddick's father Jerry, over money (a financial contract) and scheduling. Jerry Roddick knew got to get involved with tactics and match strategies. But he had a major influence in other areas, notably when it came to finances, coaches and contracts with them, scheduling etc. Apparently Gilbert wanted Roddick to spend December 2004 training intensely instead of entering charity events and exhibitions, which was a major source of disagreement - Gilbert wasn't happy that they only worked together for something like 4 days during the 2003 off-season.
A lot of people struggled to be around Gilbert for too long, especially with his tendancy to never shut up and analyse everything to death (he did that on court during his own playing career). It was clear that Graf didn't look comfortable sitting next to him, and Gil Reyes didn't look to enjoy that either. Mac joking in the commentary booth about the fact that there were empty seats all around Gilbert during the 2001 US Open was funny.