I have also had same problem in the past. I now have a brother mechanical 1500S straight stitch with a big heavy walking foot and also a heavy free motion quilt. Using this machine has allowed me to adjust the pressure on my pressure foot, and the stitch length, and the heavy walking foot seems to make a difference. However, with any machine, (if you can adjust the pressure foot tension, which on some machines you can't), I find that I make a little mock up first a "quilt sandwich" made up of some of the pieced extra blocks or partial blocks, or fabric in some batting. I practice on this first, and see where I may need to adjust things to get the nice even stitching that I need. This would be a twelve to 18 inch square or piece. It doesn't even have to be square, you just have to have it big enough to see if fabric is puckering on top and or bottom, what stitch length looks best, and if your fabrics are shifting. I find adjusting the pressure on the pressure foot makes the most difference in the outcome, and sometimes must adjust the top tension a little as well as the stitch length. For me it is worth the effort both in stitching in the ditch, as well as free motion quilting, to practice first. This was hard for me, since I always want to run ahead and get the thing done, but have found this to be a crucial step for each quilt. Sometimes battings are different. Also, I have begun to use the gloves, and the "supreme slider" which I bought online, that easily stays on your machine and the quilt under the needle part slides over this teflon slide thingy. It has a self stick bottom and I am wondering how I got along without it. Oh, it is wonderful!!! Also, I read that adding bobbin washers can make a huge difference in quilting. I bought these but haven't tried them yet. You pop them into the bobbin and supposed to give you a nice even feed. I am going to try these next. Don't give up. I had the same thing happen to me and was so frustrated. Wow I am long winded. Best of luck to you!!