Try burning even slower. I tend to not burn audio CDs over 4x. Car/truck CD players are notorious for being picky. That said, media you bought 2 years ago is probably much better quality than media you buy today, even from the same "brand".
Try to find some Fuji "Made in Japan" CD-Rs, they are getting harder to find but it is possible to do some digging (it should say near the UPC code on the media). Staples and Best Buy are good places to start. Don't buy "Made in Taiwan" media as there are a ton of companies in Taiwan, some decent, some horrible, and the goal right now is to verify the burner is working correctly (which I am 95% certain it is and this is a media problem).
Unfortunately, in the neverending quest for a buck, these companies have to sell media cheaper and cheaper; so they find cheaper and cheaper sources... so even though it's all "Verbatim" brand, it is probably made by some 2nd or 3rd tier media manufacturer in Taiwan with lax quality control (compared to the stuff you used 2 years ago).
Also, try upgrading Nero (it wasn't fully bug free til 6.6, IMHO, and they are up to 220.127.116.11a) and the Plextor Premium's firmware, they actually released an upgrade for it about 5 months ago or so, so that might help.
http://www.plextor.com/english/support/ ... emium.html