2002 Dodge Ram 1500 shutter while cruising?

[ffr]

ok so 2002 dodge ram 1500. it does have a small coolant leak, we know about that just havent got around to fixing it. The other day my mother was backing out of the driveway and it died. i put coolant in the radiator and it worked fine i think this was just a coincidence though. she said that now it is shuttering sometimes just a little while she is at cruising speed like its not getting enough gas. she said when you give it gas its fine. she said it has not happened today like it normally does but that it doesnt happen all the time. she says it usually happens in the morning but not afternoon. mornings arent cold where we are in kentucky so i dont believe that to be the case. i have some mechanics skills i do all the repairs to my own vehicle, but im not sure what the problem is on moms truck. what is the problem?