If someone can describe in more detail the problems you're seeing with save games, it would be helpful. I did notice that you can get part of the original cart overlapping with the new cart (which I will fix - apparently deleting something in a plugin doesn't necessarily delete it from the save game...), but in my own saves that hasn't prevented the cart itself from actually working.
I've been enjoying the heck out of this one, thank you so much for this mod, Maturin. The driver's banter is quite endearing and it's great to be able to stop the carriage, take care of enemies on the roads and resume the journey. Not to mention that your followers join you for the ride!
The carriage seems to be blocked when traveling from Windhelm to Riften. I hired the carriage driver at the Riften stables and he took the wrong path initially, heading all the way to Honingbrew Meadery before turning around and heading all the way back to Windhelm and then past Kynesgrove.
Then we reached a spot where the horse gets stuck in between Kynesgrove and http://www.uesp.net/maps/srmap/srmap.shtml?centeron=Steamcrag+Camp
The horse kept stoping in the middle of the road, turning around and pushing the carriage backwards, then turning around again and getting stuck. This happened quite a few times and he seemed to be permanently stuck.
http://cloud.steampowered.com/ugc/469736513757501363/F1D7E85026475A39C17A734EAE1463E52905B0A0/
Also, I thought perhaps the horse was avoiding a giant blocking the road up ahead, so I got out and attacked him. This resulted in the giant attacking the carriage and the horse fleeing, but still attached to the carriage by http://cloud.steampowered.com/ugc/469736513757506051/49D4F1C8CC8720BBB6E73AE869A3E8BB9AA1B03A/