If the walking foot and machine ate working properly you should not have to push or pull the quilt through the machine, as this will likely distort it and you will get puckers. I wonder if you are supporting the weight of the quilt on the table around you so it is not hanging off with the weight of the quilt pulling against the machine/walking foot? This will also cause problems with uneven feeds or shifting of the layers. Your puckers could also be from the quilt sandwich being loose or not basted firmly enough. I use my walking foot for all my quilting and it should give you a smooth stitch when working properly.