I've got a 2001 duramax with the allison. i was getting on it. It was fine till an hour after i got back in the truck. More than half throttle through 2-3 it kicked to neutral. After i came to a stop from limp mode it threw code P1721 for the trim solenoid B. every now and then it throws p1720 for the A solenoid. It does it every time i drive it more than half throttle. I dropped the pan. no excessive clutch material. the solenoids tested good along with the other ones. and now it WONT MOVE AT ALL. What is wrong? I need help bad this is the only truck i have to pull whith.

 

The fix 18 days at the dealership. replaced valve body. the problem internal valve body-trim pressure circuit b bore and valve worn out and damanged. The cost $2048.79 parts and labor

 

Thanks for the update, hopefully this will help out someone else.

 

for about 30% more you could have got yourself an upgraded transmission. sucks that it cost that much. thats why i dont like the dealers

 

Ugh that blows You totally could have had a pretty damn well built trans for a little more