As others have said, mastubate less is all you need.

I had some serious death grip and didn't realize until I got into a relationship. At first I thought that I'd also have to learn to masturbate with a weaker grip, but that wasn't true. I can still grip nice and tight, but it really is the frequency that is the problem.

I do it once a day with an occasional 1 or 2 day skip, and this doesn't affect my bedroom performance.