P1811 BUICK -

Question

I have a 2004 Rendezvous, I am having transmission issues, took it to a reputable transmission shop, and here are the codes they gave me:P0128, P0463, and P1811, also stated that I most likely will need a rebuilt transmission, and the valve body and control selenoid needs to be replaced..... how long do you think I can frive this car before it breaks down??? also haveing issues with getting the car to go into gear, sometimes it takes up to 20 minutes before the car will go into drive, sometimes, when I put it into drive, it will go into reverse?