Ok getting back to the topic at hand. Seeings that it sounds like your having trouble getting a good seal try calls from various mfgs. Comfort and seal is the first step to learning to properly using a diagphram call.
Prod vs hand built: You will buy production calls and think wow, that sounds pretty good, even after you are proficient on a mouth call. The problem with them lies in the fact that due to production process it is very difficult for every call you purchase after that to sound and blow the same.
You are better off buying a call that is stretched by hand: Hooks, StevePA, Legacy, woodhaven, Top
Try a couple from each of these companies and find what fits and blows the easiest for you. It might be an expensive process but the consistency betwween calls from these companies makes it cheaper in the long run than purchasing hundreds of production calls to get one that is woods worthy.
On another note once you find one or two you like, work with them calls exclusively for a period. Too many guys make the mistake of having a hundred different calls and swapping between them and never becoming proficient and understand what makes a particular work. There simply is no miracle call that is going to make you sound like a turkey, there are calls that are capable of sounding like a turkey and it is up to you to take the time, patience and perserverance to bring the turkey outta the call.