Hi folks. Bought a car from the store. Has been stuck at 27% download for 2 days 
any ideas/help would be great
Cheers Grant
Same problem here. All Meguiar Cars stuck at 19%
Try shutting the game completely down. If you don’t know how, on the desktop/dashboard use the start button (the one with the three horizontal lines) when highlighting FM5 and select Quit Game. Then shut the machine down completely, using the touch switch on the front of the console. Count to ten and turn it back on. I found this usually gets stalled downloads going again.
Yeah, definitely try that. The downloads would have timed out by now.
On day one, the content update install did that for me. (Busy day in the cloud I imagine.) I ended up restarting like DOHC46 says, and that kicked everything back in line.
I doesnt work for me. All Meguiar Cars still stuck. 
Delete your entire Forza 5 installation as well as the DLC and then reinstall the game and content. I had the same issue and that fixed it for me.
Try going to my games and apps and the queue. Then go to Forza and see if it says anything like unpause download.
OR select the Forza 5 icon and manage game or show all addons or something similar. On next screen it should show you which dlc you own and on them there may be an install or unpause option.