how come bob would nail desolation, but fuck up truckin'?
Because Truckin' tends to get tongue-twisty: "Typicalcityinvolvedinatypicaldaydream", and especially "Mostofthecatsthatyoumeetonthestreetspeakoftruelove"
But to be fair to ol' Jer, he did pretty well with even the pre-teleprompter versions of Visions of Johanna (I learned the lyrics many years ago off of the Hampton '86 one), which has many verses, although they go by a little more slowly.
Also, JG would harmonize on the penultimate line of some of the later verses in DRow sometimes. There's a spectacular one from Alpine 89.
I think part of a possible explanation for him having a harder time remembering GD songs, is that the musical arrangements were frequently quite complex, with elusive groove pockets and often flirting with the edge of technical limitations. At least that's when I begin to screw up words I've had running thru my head for decades!!