The tuck/pleating when you cross a quilting line is caused by the fabric having stretched the first time through. It helps a ***lot*** to heavily starch the top and backing before quilting. Starch stabilizes fabric so it is much less likely to stretch or distort from handling. You have already sandwiched the quilt, but starch can still help. Lay the quilt out on a clean sheet and spray starch from outer edges toward center (helps minimize overspray). A fan will speed the drying of the starch. Do this several times to build up a layer of starch on one side, then flip the sandwich and do the same on the other side.
Sandwiching using basting spray (505 and Therm-o-Web are my faves) also helps because the spray adheres the fabric continuously to the batting. You didn't mention how you basted.
As others have mentioned, using a walking foot helps too. If your sewing machine has the capability, you can try reducing the pressure on the presser foot.
Also very important is how you handle the quilt while stitching. You do not want to stretch the quilt out to the sides, or in front and back, as you stitch; this will cause the stitches to distort the fabric. If you can manage it, probably the best method is to feed the quilt sandwich to the presser foot from above. That is, you hold the sandwich up a little in front of the presser foot and let the foot feed the sandwich.
All of the above have helped me be able to stitch lines across each other without any tucks or pleats. The most helpful for me have probably been starch and handling the quilt sandwich carefully -- no tugging or pulling while stitching. I prefer using all of these tips to starting to quilt in the middle of the quilt.
Edit: By heavy starching before sandwiching, I mean using a 1:1 solution of Sta-Flo liquid laundry starch and water. This is a heavy starch. Spray starch is much lighter, even when using multiple layers, but it still helps a lot.