I dunno if other crafters have this problem, as my cooking is almost gm. I literally used 4000 leather without a single gain at 61.5 I used another 1000 and still, no gain... I am not even at 700 skill point max either.
I got a 120 tailor, took me many days to finish; you are actually better off just buying the leather at 2gp each. I was very frustrated with my tailoring. If you want advice on getting bulk leather fast, my best advice is to go to dungeons where tamers go to and just skin their kills; you get leather quickly. Sometimes I ask the tamer if they will party with me, many of them do since tamers are often vulnerable to pkers and like to have a skinner around in case one shows up.