fuel filter. The filter is plugged. The pump can make enough to keep up with idle demaond but unce you start using some real fuel it cant keep the float bowl full.
I don't care that you changed it a couple months ago change it again
I have had this happen on both my K5's. Took them wheeling . The sediment at the bottom of the tank breaks loose and clogs the filter. On the one truck I had 2 weeks in a row had to change filter every other day. Finaly got it out of it's system after about 2 months. When it sits over night some of the sedimate will settle to the bottom of the filer and it will run ok for a little bit till it gets stired up again.