What sluice do you use?
In larger streams and rivers, i find running the primary material through the 48" sluice with the supplied grizzly (about 3/8" openings) first, and then running the resulting concentrates through the 30" sluice modified with screen over the grizzlies (reducing to about 1//8") by the time I din the second run, all my fines were easily panned out ...