When I had this problem... new exhaust manifold, intake/exh manifold gasket, (IF you have obvious exhaust leaks) upstream o2 sensor, cleaning the intake air temp sensor (looks like bolt with a wiring harness coming off the manifold near the firewall), all contributed to eliminating the cold stumbling problem. Biggest things? o2 sensor and IAT. My IAT was plugged with black crud from the PCV something awful.
My original cat was hollow, putting a cheap one on and the downstream o2 cleaned up the CEL.