Why will a truck not start on cold mornings when it warms up a little to 60 degrees it starts fine it sometimes also helps if you take your air filter out it is a 1998 Chevy s-10 2.2l fuel inj?

It would seems it is not getting enough fuel. This truck is fuel injected so I would replace fuel filter and then check your fuel pump pressure. Because the vehicle needs more fuel when it is cooler, the problem is aggravated as the temp drops. It is possible your fuel pump is at the early stage of getting weak.