Two things about the upper tunnels come to mind... the first is that there are 3 versions of the instance available at zone in. From top to bottom on the list they are normal, hard and very hard. Are you choosing an option other than the top one? This would make the mobs tougher than they need to be...
The second thing is that even in the normal mode, there are some group mobs in the instance but these are all easily avoided if you are solo or just choose to avoid them.
Regarding chest drops, I have always found Splitpaw to be one of the best places in the game to do solo loot runs. A run through the upper tunnels used to take me about an hour and netted an average of a dozen chest drops. Even if you vendor the loot, a dozen adepts and rare recipe books an hour is a pretty good revenue stream