I think the bigger issue with the car is how a hardened survivor such as Daryl was dumb enough to take his eyes off the road for so long. It's an easy mistake to make, but it seems like he should know better. If he or anyone else had been paying attention, they could easily have stopped, turned around, and rerouted.
Also, at some point they shouldn't be able to drive anything. Gas goes bad (oxidizes) over time, and I doubt any new gas is being produced.
The other thing that bugs me about this episode is the notion that antibiotics are some huge cure. It seems uncertain to me that the disease is even bacterial (it more closely resembles real world viral infections to me). Even if it is, antibiotics really only give a boost to the immune system in most cases. Unless some of these people are able to survive by their own accord (as happens with even very bad infectious diseases), antibiotics seem unlikely to make a difference. Of course, we haven't seen anything happen with this yet, it just seems to me that Hershel's plan is unreasonably optimistic and he should know that.
The show does continue to have pace and flow and there's a lot of interesting stuff going on.