i use one quite a bit, not a PRO at it but same as you I know a few guys that can make it sound absolutely PERFECT!!
i can work it decent, have killed a few birds using it but agree it was by far the hardest call to learn to use. Took me 3 years of working with it to feel confident in taking it out to the woods.
suggestions? keep practicing is about all i got. I equate it to feed calling on a duck call. You have to hit the "diga,diga,dig/tica,tica,tica" as fast as you can while starting HIGH and decreasing in pitch.
the right tube and reed makes a HUGE difference as well. Find one that fits you mouth where no air leaks out the sides or top of the reed. i have about 10 different tubes but can only really call on about 4 of them, for some reason the others just dont fit right.
i know that is not alot of help but it is a hard call to have suggestions...
what issues are you having on yours, that may be a good starting point