We’re not a file host, so I can’t offer myself. But regardless the “Slow Upload” speed, why “No sales” is a problem you think is related to the file hosting? I mean if you moved into another host, would the people start buying premium? I think it makes no difference, except if you think the file host is shaving sales which is totally a different case.
I am not an expert in file hosting industry, but I am just asking to learn, what is the relationship between the file host and the sales, because I think your sales are related to your visitors and not the file host itself, or maybe there is something else that I don’t know about, yet.