And just to add to what Blackhorse 70V said... make sure that you've burned an audio CD rather than an mp3 CD.

Even though you might've downloaded mp3 files, you might still not be able to play an mp3 CD (different to an audio CD) in your truck - lots of older players won't play mp3 CDs.

It's fine to download & burn mp3 files but in your burning software's options choose 'audio CD' instead of 'mp3 CD'.
Then see if it'll play in your truck