09 GMC Sierra Denali 291K struggles to start only when cold. When attempting to start it will try but dies, once started it idles rough and the exhaust has a strong smell. After running for a few minutes, it levels out. It appears to be firing but something is causing it not to start. The truck cranks fine after it warms up, at times after driving when starting it will crank but not a strong start, it barely catches and soon idles fine. I have replaced the fuel pump with new wires and plugs.