My 95 B2500 v-8 (108k miles) was just tuned up and now bucks like someone is hitting the back of the van when driving at 60-65mph and around 40mph when at a steady speed or slight deceleration. If you give it gas it goes away. The garage that tuned it up said it's not the engine but might be a torque converter.
Another mechanic checked for codes and came up with nothing. I have made an appointment with another garage for next week since no one has the time without an appointment to test ride it with me.
Some one mentioned it might be a throttle control issue. Could it be??? I have just read a thread about u-joint problems; but, I have had that problem in the past with a 85 Ram van. I don't believe it is that.
Anyone have similar problems like this before?? I plan to hold on to this for years to come. It was great to have when the kids were little and now I use it to help the kids that have moved out to cart things around and tow a two canoe trailer. I really like it.

 

Were the spark plug wires changed, or rerouted in any way?

 

I would hopefully think they are in correctly. Another garage hooked up a small analyzer and no bad codes appeared. I drive approx 7 miles one way to work daily. It starts up fine and smoothly and drives smoothly until those speeds are hit and bucking or chattering occurs.

 

Have the fuel pressure checked to make sure the pump is pumping enough fuel.