I have a 2011 Chev diesel with an Allison transmission. Truck has about 168K miles on it. No problems with transmission until yesterday. Went to leave and the truck would hardly move. Tried different gears and changed the xfer case but nothing helped. Went out today and it won’t move at all. I tried to check the fluid but the way it is setting is hard. I did add 2 qts. fluid just to see. No help. Did not throw codes today. Yesterday it thru P0708, P0712, P0751, P0972, P0974, P0757, P0975, P0761, P0979, & P0980. Thoughts?