Yup - I'm having some similar results.
I have to say that, despite the heat and relative dryness in my area (which is very localized, as the rest of the DC metro region has generally gotten a lot of rain), my garden is going gangbusters. I had plants last year that were pushing 12', with all of them (aside from Romas) being upwards of 8' easily, with a lot of tomatoes on them, to boot. This season I was concerned that things would slow down with all of the heat, but since most of the tough weather came earlier in the season than last year my plants have had time to recover. My San Marzanos are pushing 5', as is my remaining Mortgage Lifter. My Brandywies are 7' and 9', respectively, while my Cherokee Purples are around the same. I have one Valencia that's already outgrown its 10' bamboo stake!
And despite all the growth I mentioned above, I'm finding a lot of new growth from the bottoms of my plants right now. Usually what I'm seeing is new, strong stems developing from the ends of trusses. It's amazing - I'll be out there one day, looking around, picking, persusing, but not seeing any anomalous growth. I then go out the next day and I see new stems and flowers where I didn't see them 24 hours earlier! I also have on Valencia in a pot that developed blight, so I chopped off the top of the plant above the remaining four tomatoes, leaving about 3' at the bottom. I did this about four weeks ago. Lo and behold, a new stem started growing from near the bottom and it now has flowers on it.
It's been a wild season. Of the remaining ten plants I have, I've harvested upwards of 50 pounds of fruit, easily. I'm in a relative lull right now, as the flowers that developed during the big heat in June and early July would have been good-sized fruit by now. But I've been seeing a good amount of fruit formation in the last couple weeks, so I'm hoping for a strong push as the season starts coming to and end in October!