Any regular hammer will work on thick seams as well... just pound it a bit and it will sew easier! not sure if that is the issues, but if it is this might help! :)

I had a problem with my Espire when I was sewing a fleece robe. The belt carriers were loops. The fleece was very thick where the loops were set into the seam. The machine kept 'leaping' over the loop ends in the seam. I finally hand stitched the loops in place.
I haven't researched why this happened yet but know with the next fleece robe I make I will apply the carriers to the surface of the seam line instead of inserting them into the seam.

I don't see any way of adjusting the presser foot pressure. I will look into using the special foot mentioned but wonder if it will work on fleece.

I've shortened some corduroy pants and sewed fine over thick seam lines. I've not had this problem on regular piecing cotton.

You mentioned you changed the needle a few weeks ago. Have you done a lot of sewing since then? I generally change my needle with each new project - sometimes sooner if it is a large quilt.

I actually have this accessory for sewing over thick seams. it was for my Singer. worked fine.http://www.thecolorfulworldofsewing....mp-Jumper.html

Someone mentioned something about using the foot that has the little spring on it. As it happens, that is the foot I use all the time. I've never used that feature so I just tested how it functions and if you push the little spring button, it makes the foot rigid (so, when in normal use without engaging the spring, the foot flexes front to back--not side to side of course). I have already finished the quilt so I will have to test out this function tomorrow sewing some scraps together.

Page 43 of your sewing manual for the Espire discusses heavyweight fabrics. Those seams should glide through the machine.
Your presser foot lift lever should have 2 position levels. All the way up for thicker fabrics, or seams in your case, and halfway for thinner fabrics. Your machine also has an Automatic Fabric Sensor. This should be turned 'ON'.
If you have used your needle for hours prior to the point you are at now, it may be good idea to change out your needle. Cheap trade-off to eliminate frustrations and to sew smoothly.

I have a Brother Innovis 2000 and the same thing is happening to me. It can't seem to make it over anything even semi thick. It skips stitches really bad and then I have to attempt to sew over it again. I'm working with a tapestry fabric and it is really acting up. This was not a cheap machine. I'm going to try to check to see if I have the presser foot with the spring.

Here's an easy trick if you can't adjust the presser foot lift higher: Stop just in front of the seam intersection, needle down. Lift the foot and slide a piece of cardboard ( about 1/8 in thick) right behind the needle, foot down, sew over the intersection, take out the cardboard and continue. This is your DIY jeans-thing.

I was sewing a handle for my tote bag and kept having the problem with the skipped stitches. Pulled out my owners manual and it recommended a larger needle to get through the thickness - problem solved.