06 with 5.4 and AT. It shudders in overdrive during light to no acceleration. I was told it was the converter. I was also told by a technician in a trans shop that the Trans-X additive for hypoid oil in a posi-trac was ok to use even though the back of the tube says "Not safe for automatic transmissions". Does anyone know if this is accurate or if the guy was just blowing smoke? Thanks

 

I have used additive for the posi trac differential before and it did work, but I would recommend just changing the fluid first, most of the time that will fix a mild converter shudder.

 

Thank you for your input. I really do appreciate getting info from a tech and not just someone who is repeating what he heard elsewhere but doesn't really know.

 

x2 on this. I had a pretty bad TC shudder in my 01 7.3 and a fluid and filter change made it go away. Although, the tranny did end up blowing out about a year later. It didn't have anything to do with shudder though.

 

The 2007 I am test driving right now does this as well. I noticed this accelerating from 40. It has me a bit concerned.

 

I would inform the dealer and let them know that it has to be fixed before you consider a purchase.