What might be the cause for the truck to jerk upon take off a couple of time and at 40 mph when the transmission shifts? The rest of the time it runs smoothly down the road. Any other causes beside the transmission itself?

 

Sure it could be something other than the transmission. I think the shift is controlled by a computer module so if there is a bad connection or a problem there, it could cause stuttering. Fuel filter, drive shaft, a lot of things can cause what you describe.
Hopefully, not the transmission.
Try driving the truck in 1st or 2nd instead of D and see if you have a problem. Also when it starts at 40, put it in neutral and see if the shaking continues. If so, it is most likely not the transmission but mechanical in the drive train ( U joints etc.).

 

What year model......engine....transmission..???????

 

1999
4.6 L
Automatic

 

What's the average mileage for a transmission?? I'm at 120,000 miles.