I first realized improvement not on how I felt at the end of a ride (or hard hill) but on how quickly I recovered. My recovery rate kept improving until the 8miles became easier. I also have a downhill to and up hill from commute. The last bit is quite steep and I find that I can either wear myself out and bike the whole way or stop a 100 yards and walk. I figure the 100 yards acts as a cool down.
Eric