Thank you very much for your replies and advice

modus.irrealis - I definitely have the problem of looking up too many words. If I'm only 70% sure of what a word is I look it up and usually end up being right... I suppose I should have more confidence in what I do know, and perhaps try to figure out more words based on context. I'm kind of a perfectionist and I think that slows me down a lot.
I think a part of my problem is the way my school does Latin, you don't do any serious reading until the third year. The first two semesters are just Wheelock's. In 200 I read some Caesar, Cicero, and Catullus (Catullus is awesome!), but the assignments weren't that long. 250 was the Aeneid and again the assignments were pretty short - 20-40 lines typically. I took Caesar last semester...we read book 2 of the Gallic Wars and it was not terribly challenging for the most part. I was able to sight read a Caesar passage pretty well on my midterm and final. We also read some Sallust which was harder but became easier once I got into it. This semester we started with Seneca's Apoco... which again was difficult at first but became much much easier as I went along. Juvenal, however, is not getting easier. His use of vocabulary is extremely extensive, and I indeed feel like I'm "cracking a code." I've never had this much trouble with Latin before... it's taking me hours and hours to do these 100 lines. Is it worth explaining to my professor that this is a little advanced for me? Everyone in our class is at different levels because I'm studying abroad in Athens, so the students are from different schools, and some of them have read significantly more than I have.
Damoetas - I am pretty particular about my translations, which is probably why they take so long. I want to know the function of every word. If there's a subjunctive, for example, I
have to know why. And I do consult a translation, but obviously most translations don't reflect the Latin grammatical constructions perfectly. I think I typically do a good job of comprehending the Latin - I never write out translations; just vocab. And when I translate I try to go back over it a couple times.
I don't really have time to read anymore Latin than I'm already doing for class - not only does it take forever but I'm also in four other classes, including Ancient Greek and Modern Greek. But I'd really like to perfect my Latin this summer. Any recommendations on what to read?