Do you have a thou gen 1? If so, try looking at the end of the gearbox shaft where the clutch basket sits, there should be a cap in the end of the shaft to control where the oil goes.
On my old 98 R1, this came out and fell into the bottom of the clutch basket, and the oil 'poured' over the clutch plates causing drag so severe that at a standstill, the bike wouldn't stop with the clutch in and first gear engaged, it crept forwards quite a lot.
Engaging first was an absolute barsteward! It jumped forwards on engagement, and occasionally stalled. Might be worth a look to see if the cap is still there. Its only a push fit, and I just tapped mine back in place with a hammer and that solved it>
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