Even if you get the electronics right in the transmission, you still have to deal with the electronics on the outside, and that is where even a "perfect" transmission builder has no control of what the customer is going to do with it or what changes he might make that can/will effect his transmission work, once it leaves the shop. As for me, I have to make sure that the transmission is going to do what I say it will when it leaves my shop, and as stated earlier, I have no control of what that person might do in the future as to "changes" that might effect the the electronics in some way. That is a "very good" reason for me to use the vacuum modulator.