I've found that when some designs so are so stitch heavy that they tend to have several layers of stitches on top of each other, if your design software allows step through the colors and see if there are any you can skip. One set of cars I got was so intense but found that several colors were stacked on top of each other, skipped the underlying colors and they came out great. Won't always work but if worth a try.......;-)
I think the design I am struggling with has that same issue, too many layers. I may try skipping some colors in parts. I do have a program that will do that, and my machine will skip colors also. Thank you.
I can't tell you if there is a free program, but the program I use to organize my designs includes Density Works. Studio Plus (now Studio Three includes several (hoop works, size works, density works, etc) They cost a bit but worth it in the long run.
I have thought that may be a good investment. I'll have to check it out. I think several of their programs look good.
Thank you.