It's totally cringe, and the first couple of times you have to do it it'll be uncomfortable. But growth happens at the edge of your comfort zone and you'd be mistaken that everyone's a born natural at it. Most people have to practice at it in order to get good at one. Few people just born with it. So what, you're not one of them. You weren't born knowing how to program either.
As far as slimy, I mean, yeah, don't break ethical boundaries; don't lie, don't take credit for other people's work; and it'll be fine. The ick feeling comes when we see others do amoral things like that and get ahead, but all you have to do to avoid that slimy feeling is to not lump all self-promotion together, and then just don't do the unethical bits.
Lying about the true cost of software and taking credit for your employees work is the basis for consulting. Some might term these as Profit, and Reputation. But that's sales for you.
As far as slimy, I mean, yeah, don't break ethical boundaries; don't lie, don't take credit for other people's work; and it'll be fine. The ick feeling comes when we see others do amoral things like that and get ahead, but all you have to do to avoid that slimy feeling is to not lump all self-promotion together, and then just don't do the unethical bits.