I have a 2000 WR 400, it's got YZ Cams, an FMF Q Pipe and about 100 hours on it. For about 30 hours now it has been exhibiting an odd slipping sensation, but only in fifth gear. All the other gears pull great. It only happens under load, not when coasting. I replaced the clutch basket, clutch boss, friction plates and clutch plates with springs. This did not fix the problem. What could it be? My suspicion is that fifth gear itself is damaged, or possibly a shift fork? But I don't want to crack the case until I've eliminated everything else. Any help would be greatly appreciated.