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.