Transmission Shudder/Clunk while towing
 

I have a 2001 SCrew 5.4L with 42K miles. I have had no transmission problems since new. I just recently bought a buggy (about 2500lbs, flatbed trailer) and while towing it up some grades the tranny began shifting strange. When I started heading uphill (in 4th) and when it would normally downshift into 3rd, there would be a bad shudder for a few seconds and then it would clunk into 2nd, then shift up into 3rd. I tried driving with the OD both on and off, as well as trying different throttle positions (floored, letting off the throttle as I started up hill, etc). Nothing would work and it would do this every time I headed up hill. Speed was 50-60 mph. I have never had this happen before, and have tried to duplicate the problem without the trailer but can not.

I took it into the dealer and was told this was normal.....

Does anyone know what this could be? I had my fluid changed at 30K and I have checked the level, I know the conditioner was put in. In searching the boards it sounds like maybe one of the accumulators???

Thanks!!!!

It's difficult to say just what is happening. It could be involved with the fluid change, type of fluid used or a marginal transmission problem that only shows up with an extra load.
A good trans shop should be able to pin it down given some time.
I have looked on the Sonnax website and they give a lot of info on various problems that the average owner never knows about on how to trouble shoot.
I'm not surprised that a dealer dosn't want or dosn't have enough expertise to run this down.
In any event don't try to use OD to much in an 'excessive' shifting situation while pulling a trailer.
In any event be prepared to spend a little money getting a solution to it.


Extra info: There can be a problem with how the PCM handles the shifting that would be load sensitive.
Sometimes reprogramming may solve it.
There is a company that offers a shift modifying board to add to the trans to help this situation.
Apparently is is a know problem with some transmission/PCM combinations.