As you said "ever since..." I was under the impression that the chain was replaced then, and I missed the comment about it happening on the old chain. Given the new info, the only thing that would be consistent across all gears and produce the symptoms you describe is the freehub. This is simple logic - The pulleys would not affect skipping, as the chain is not under tension there. A cassette cluster will never skip on all gears with a new chain, and chainwheels would show a problem only under extreme wear or where one tooth has a problem, which would occur every rev. The chain is not it as the problem continued with a new chain. The only component left that is parr of driving the bike forward is the freehub mechanism. I would suggest you replace it.

p.s. "tawt"?? Is that like Tweety's "I tawt I taw a puddy tat" (before many folks' time)?