I agree with the MAF sensor as a possibility. What engine does it have and is the check engine light on? The mass air flow sensors a lot of times will not set a trouble code/check engine light. The 5.3 and 6.0 liter engines have had problems with intake gaskets leaking vacuum as well. We see more problems cold than hot. When they are cold they leak more and run rough and wont idle well, then when they warm up they expand and seal again. If you have codes read somewhere see what they are and let me know, I can further assist you in the diagnosis. If it has a p0171 and p0174 it is an intake gasket leak. You will probably have p0300 missfire codes also. Let me know if you need more info. You can PM me if you want. Good luck.