'03 SMB 4X4 with 140,000 mi. Transmission is a 4R100. Ran OK but it had gotten us over some very serious grades, through blow sand and snow, allowed us to do some very aggressive crawling and survived two near meltdowns. We are also towing a 29' Airstream much of the time. Took it to Aberdeen Transmission, Aberdeen, SD - a shop owned by a friend. They found a number of emerging problems in both the torque converter and trans. His opinion is that the 4R100 is one of the better transmissions on the market for one ton vehicles but, because of the weight of the SMB, they should be rebuilt and beefed up after 120,000 mi. One of the key problems is due to Ford's use of aluminum parts in the trans. The material is too soft. They all showed extreme wear - especially the fluid pressure control valve. Cost was $2100 for the rebuild and upgrade with a one year warranty.