Better than the real thing, really.

IIRC, the solo also continues through the credits

According to an interview with a Minneapolis musician named Andy LaCasse he played the actual solo, which according to a transcript I came across awhile back went like this:

"'d gone to college with Mike Nelson who was the star of the show at that time and…the name of the particular movie that they were using in this episode was "The Dead Talk Back" and Mike and the robots… well one of the robots 'Crow' had decided that they would become The Grateful Dead. So they all have, you know, beards and crazy tie-dye t-shirts on and there's a song that they play called "Cosmic Freight Train." And then Crow, one of the robots, takes this epic guitar solo. And he [Mike] couldn't get a proper bad guitar sound out of the synthesizer he was using, so could I please come and play a bad guitar solo for them… So I walked in with a Stratocaster copy and a Big Jam Spit-Wah pedal, which was a little orange pedal about this big that did, you know, that quack-like-a-duck sound, like an envelope filter thing. Like Jerry Garcia would use, 'cause Crow is being Jerry Garcia.. So they've already filmed it, they've already taped it. So I'm watching a monitor, and they said, "Just follow Crow's hands and play along." [laughs] And they said, "And make it really annoying." So I took a pass at it and I get done and they're giggling, and they said, "That's pretty good. Can you make it even more grating?" And I said, "Yes" having no idea how I was going to make it more grating. I made a couple adjustments, and they said "Every once in a while go [sings] 'wamp wah wamp wah wamp wah' just over and over because that's what Jerry does. When I think of Jerry that's what I think of him doing." I said, "Ok. I'll do that." And the next take they said, "That's awesome. It's really really long and painful…" They liked it so much they had me do the same thing over the credits."

I always skip the skits, but this cracked me up.