LOVE Pitt Bulldogs! I fosted three for local shelters. One was probably Lab/Pitt mix. All were extremely gentle with people, not well-socialized with other dogs. Since they were rescues, I cannot speak for their early years, but they were all successfully adopted out and lived their lives as family pets.
Bull dogs get a VERY bad rap. If Poodles were reported for all the toe-bites they inflict, they'd be considered much more problematic, in my humble opinion. They problem with a badly socialized bulldog is that it can inflict great harm because they are such powerful dogs.
My daughter has a Boxer/Pitt mix adopted as a five year old. It took us a couple of years to socialize him to other dogs, and we don't leave him unsupervised. However, he is playful, gentle, and responds to commands to calm down if my year-old Labs get him worked up.
I agree with all comments here...Your dog needs to meet as many people and other animals as possible in an environment where he can feel safe. Don't be surprised if you get grief from other, less-educated dog owners about the dangerous animal you are harboring. Be prepared to have him on a leash ALWAYS in public. You may not be allowed to turn him out at dog parks, etc.
But you will be rewarded with one of the sweetest, most loyal family friends you can imagine. There are some excellent books about the Bully Breeds...their history and natural instincts. Though this is not the forum for that, I'm really glad to see the support you have here from Lab owners!
Helen Keller's dog was a Pitt Bull....So was the RCA Victor Dog used in their victrola ads. The breeds was at one time, the most popular family dog in the US.