The other day i was pulling a pretty good load (25' goosneck w/337 Bobcat Mini-X), pulling a pretty steep slope in 2nd gear (as i was stopped at the bottom of hill) and as i was nearing the top of the hill i noticed/felt the trucks power/rpm's surging at around 24-2500 rpm's? At first i thought i was imagining things, but when i saw the tach move as well i knew i wasn't. Any ideas?

It is a 07 5.9 w/manual, edge/att., w/around 65K on it. If i had to guess it felt like it was lacking in the fuel dept., maybe fuel lift pump?? I know those are a problem on these trucks? Thanks!!!