I've noticed that I can d/l without problems, but u/l is another matter.

I uploaded a torrent to a private tracker, but when people try to d/l from me I get odd behaviour. The speed fluctuates. It would reach a max, decline to 0 for 10 seconds or so, and repeat the cycle. All the peers say Chocked Yes, Snubbed Yes.

Any ideas how to solve this?

Version ?

Upload should normally work, the fact that you see Choked and Snubbed is not much of a problem for upload.