Personally, controlling my breath helps alot. I have some problems aswell, I use Funhalver often lol.
I did find on the Fleshlight website while looking into different sleeves, under the Stamina training unit there is a FREE PDF file on FREE e-guide for increasing your stamina. Havent read it much but I seen it mentions controlling your breath and tips on it aswell. Dont own a Stamina unit(Yet lol) but it looks intense. Hope that helps in any measure. 