Hard shift from 3rd to 4th...

[sfpcservice]

So after towing our 3500 pound trailer on a few trips I noticed that when the van has to downshift due to a hill or headwind from 4th to 3rd, when it upshifts back into 4th the shift tends to be hard and sends a shudder through the van. I always tow with the gear selector in "4" so I'm not sure if this is a gear or lockup, but I'm assuming its the gear because this is immediately after the rpm drop from 3rd into 4th. Anyone ever experience this? Should we be worried?

[brian_bp]

I don't knw how concerned I would be, in part because "hard" is so subective.

To distinguish between a gear change and a torque converter lockup clutch engagement, I would consider the amount of speed change. Locking up is typical not much more than a 10% speed reduction, while a 3-4 up shift is roughly 25% decrease.

[sfpcservice]

I think its definitely a gear and not the torque converter lockup. It feels like someone dumping the clutch in a manual when the speed wasn't quite right... It shifts as smooth as always without the trailer though, so it just seems to be related to shifting under heavy load.