1998 Oldsmobile Silhouette My van feels like it's running o

My van feels like its running out of gas very inconsistently. Whether accelerating or cruising it jst hesitates (loses power then comes back, loses power then comes back). It will do this at 60 mph cruising or at 20 mph under acceleration. Also it does this with no pattern, it could go 2 days without it, and another day it might do it several times. Cold or hot makes no difference. It does not feel like a transmission problem and the check engine light is not on. Where do I start troubleshooting this problem?