hard start and rough idle

[EKlem]

About a month ago my truck suddenly began to take a lot of cranking(~10 seconds with some pedal) to start. I looked through the threads here and figured that I had leaking fuel lines. I looked at my truck and saw that all the fuel lines that I could see were fairly new(I bought the truck a year ago) so I didn't replace them. I did notice that my fuel filter had a manufacturing defect and leaked fuel. I replaced it and the problem seemed to go away for a few days.
Now, the majority of the time, it takes a fair amount of cranking to start. It does not seem to matter whether the engine is warm or cold or what the air temperature is(it acts the same from 0-50 degrees). When it does start, I have to stay on the throttle for a little while and it does not run well. The truck shakes a lot and I get a lot of blue smoke and sometimes a little black smoke. After driving it for a few minutes, it runs fine except sometimes at idle. Sometimes it will idle about 100rpms below normal(900rpms) and shake the truck a lot. If I rev it a little, it will idle fine after I take my foot of the throttle. So my question is, is this an air leak in the fuel system or something else? If it is an air leak, should I start by replacing fuel lines or is there something else that would cause this?
Thanks in advance for the advice. Sorry if I am slow to respond to questions but I have very limited internet access until I get back to school when I will not have time to fix this.