When going uphill and the transmission starts to downshift the car starts bouncing like its on a washboard road. If I press the accelerator it smooths out. and if I can tell when it's going to shift and press the gas it is OK. I have replaced the fuel pump and all filters so I no it's not a gas problem. The accelerator cable seems to be slack to me but the only time it does this in on a hill.
It only happens when going uphill and when the transmission is about to shift to a lower gear. If I press the gear the accelerator it does not do it. Also, if I am paying attention and can tell it is about to shift and press the accelerator it doesn't happen.
At other times the transmission works smoothly and the problem doesn't occur.
Hope this explains the problem so you will have an idea of what the problem could be.
As for the question on the gas, the tank was lowered, the in tank pump was replaced with a new pump with strainer and the outside filter was replace with a new one.