I have a strange problem. I have a 1996, 2.3L and the truck has always started without any problems until 2 weeks ago (middle Jan). It will not start if the temp outside is 15 degrees or colder. If it's warmer than 15 degrees it starts just like it always has. The local mechanic has replaced the
fuel pump
fuel filter
plugs
wires
cold/hot temp sensor (located by the thermostat)

He has kept it over night for a few days and starts it in the morning to see what happens. He told me he has no idea. Has anyone had this problem? I would appreciate any help at all