do the basics below. if nothing broken internally or clutch pack components worn out....this fixes shifting problems 90% of the time. the procedure though fairly simple MUST be very concise and accurately done. if you can't do it get a local sportster expert to do the job. it is one and the same. also your bike is FIFTEEN YEARS OLD. you mentioned NOTHING regarding mileage, abuses in the past, clutch history, nothing! service manual covers it all but here it is simply put:
1-drain primary fluid for at least 1 hour...refill with 1 quart ONLY of Amsoil 20-50 cycle oil OR mobil-1 20-50 cycle oil. i prefer amsoil.
2-remove derby cover and chain inspection cover---both on primary cover. loosen clutch pack screw 1 full turn then loosen clutch cable adjustment barrel and jam nut. loosen barrel approx 3 turns.
3-remove clutch cable from lever and perch. completely clean and lube cable. if worn/frayed at lever/perch area replace cable.
4-lube lever pivot points on perch.
5-reassemble cable and NOW adjust both the cable and clutch pack screw. manual covers it and simple procedure.
6-replace derby cover.
7-adjust primary chain at room temp after all above steps have been performed. NOT building space-ships here. simple 1/2 inch cold chain freeplay up and down sufficient. replace adjustment cover.
now test!