Overcrowding may not be allowing the plants enough sunlight.
I never prune my tomatoes unless we are right at the end of the growing season and I decide to remove the branches with only flowers. I may decide not to water them during the final few days also. That will hurry along ripening before 1st frost.
A Brandywine seems really beyond the "reach" of my gardening environment. If everything else is equal -- growing season warmth is what brings about maturity and ripeness. Here is a link to Weather Service information on Growing Degree Days (click).
You may see your city or one near you with a comparable climate.
I can tell you that Houghton in Michigan's Upper Peninsula has had about a much growing season warmth as here. I claim that we are in competition with Devil's Lake, North Dakota but I'm sure that folks there aren't aware of it and folks here can't do much about hurrying the tomato crop along
. By the way, we have a lot of catching up to do to catch Devil's Lake this year!
I think there may be a lot of imagination (for want of a better word) that goes into the Days to Maturity concept. I guess, 1700 Growing Degree Days are kind of a general rule of thumb for maturing most tomatoes. The "other things being equal" is a bit of a stretch. For example, I'm fairly sure that the tiny handful of tomatoes that I've harvested so far (none the size of a tennis ball) are from flowers that set fruit while the plants were still in the greenhouse. Once they went into the open garden, they had too cool of temperatures to produce fruit until fairly recently. They should be along but there will just be dribs and drabs of mostly cherries for awhile yet.
The Celebrity looks like it would be a good choice. A standard for me for nearly 20 years has been Big Beef. They are usually listed as a 73 day tomato. You may need to go to a 65 day tomato. There are quite a few.
I once lived at several hundred feet higher elevation. We hadn't yet been given the chance to grow so many varieties that came to us from the former USSR and eastern Europe. About the only tomato that would ripen in my garden was Sub Arctic! Some seed companies list Sub Arctic as a 42 day variety!
Don't give up!