Been spotty for me this weekend too... slacker song 'loading errors' having to hit the retry ... gets the song going 50% of the time... other times having to skip to next to get something to play.
But then again, I've also been seeing an unusual amount of network degradation / dropping from LTE to 3G and heavens even the dreaded "E" edge which means basically 2 bits per second throughput. And then bang back to LTE!
It might be a move on Tesla's part to degrade the service to make upcoming Tesla Tunes look like a more attractive option having content that Tesla manages and can control the experience to the car better than Slacker can.