I just finished a 1,100 mile trip with 9200 lb trailer, about 70 MPH, using tow/haul. The last 50 miles were two-lane through small towns. It started "clunking" really hard when it downshifted into low gear. Take it out of tow/haul and all is fine.

Is this going to cost me a ton of money?

 

How did it shift into low when in tow-haul earlier? How many miles on your truck and what mods?

 

Except for the exhaust, no mods. It has 62,000 miles. It did this a couple of time before when I was pulling my 14,000 RV, but that was at aound 5,000 miles. This past summer I took a 2,500 mile trip with RV and it never did it. This time it only did it only did it at the last few miles of a long day.

 

I wouldn't worry about it. Sometimes the learning program in the trans controller doesn't do what it should and makes a hard shift. It should learn it's way out of it, or you could disconnect both batteries to reset it quicker.

 

My 2003 CC DRW 6.0 did the exact same thing. When downshifting to low in tow/haul it slammed so hard I worried about collateral damage. Ford reflashed (reprogrammed I guess) the computer and it never did it again.

 

Thanks for the feedback. I made the return trip with 7,200 lb trailer and it never did it again. I'm not going to worry and just get some better shifting when I can afford Matt's tunes.