FYI- J Crew makes clothing for slightly less fat fatties. There is no point in paying J Crew prices if it doesn't fit well.
You have to stick with stores that have Athletic/Vintage/Muscle fit. Try Express, H&M, United Colors of Benetton, and Zara.
Let me know if you find a brand of dress pants that actually fit well (machine wash only). The pants I've tried on either fit poorly or for some reason show off the crotch bulge too much.
JCrew fits my body nearly perfectly, which looks GREAT, but having worn oversized shit my entire life, I miss the ability to dance and jumping jacks comfortably in my button up shirts.
What kind of dress pants you thinking of?
I'm VERY low key on pants (I refuse to pay over ~$50 for pants - they're just pants?), and have been pretty happy with Gap "dress" cotton and wool-blend pants. They're pretty light material, slim-ish and have good structure.
I use to shop H&M and their stuff did fit, but I've been noticing the shoddy quality more lately, and some of it's way too fashion forward for me. Speaking of, Gap has been sucking for over a year on the tops: shirts are uncomfortable (material), cut for fatties, and the designs are just "off".