There are certainly a number of things that you can do before going to the expense of changing pickups, most of which may have a bigger impact anyway.
The cheapest option is to look at the EQ settings on your amp and unfortunately you don’t say what you’re currently using so the only advice I can give is not to use a scooped sound. If you want to have some cut, you need mids, especially upper mids.
Next I’d go with the option of an Overdrive pedal and use it as described by Agent Orange. This can be a really cheap and effective way of manipulating your tone. Most players use too much gain anyway, me included, so dial it back a bit so that you have a tone that is certainly distorted but not overtly so then kick in the Overdrive. Something like a Digitech Bad Monkey can be bought for just £25 new and is incredibly effective for the money. The other guitarist in my band still swears by it and when I was looking for an Overdrive recently I went straight to the Hardwire Overdrive by Digitech, which can be had for £45 new. The point is that it’s an effective way of tightening things up without having to spend a fortune.
After that I’d go back to EQ but this time I’d get an EQ pedal. I use a Boss GE-7 and I’ve found that it completely transforms the way my amp sounds and one of the effects is certainly greater clarity. You can pick these up on Ebay easily enough for about £40 and it’s a great investment. In fact, Overdrive and EQ are two pedals I simply couldn’t live without these days.
Once you’ve tried these options, things may get a bit more expensive but next up I’d look at the speaker you’re using. The speaker(s) you’re using can have a huge impact on your tone, probably a lot more than a new pickup will. If you just use a 1X12 like me, this is a very cost effective way of transforming your tone but obviously, if you use a couple of 4X12 cabinets then it will get expensive quite quickly. When I switched from my old Blackstar amp to my new Orange amp it took me quite a while to dial in the tone I wanted and a lot of that was getting used to the new speaker (Vintage 30) but the effect of having this different speaker has been dramatic. I cut through the band mix far more than I ever have done before, so much so that I am probably now on a lower volume setting and still being heard more. The speaker you’re using is often overlooked as we talk about tone but in my experience it has a far more profound effect than any pickup I’ve ever used. Put it this way, I top quality pickup going through a poor speaker will sound terrible but an average pickup going through a top quality speaker will still sound impressive. In an ideal world of course, you have your Holydiver going through a great speaker and if you also tie it in with the other suggestions here you’ll find you’ll be much happier. For a cheaper option to Celestion speakers, try looking at these guys who have an excellent reputation:
https://wgs4.comIf all of the above fails, and I seriously doubt it will, then you’re down to the more expensive options of changing pickups or changing your amp. If you end up changing pickup, then I’d look at the Miracle Man but if you like the Holydiver, I’d certainly be trying all of the above first. Finally, keep in mind that a good pickup, like a good valve amp, needs to breathe to really show what it can do. The last new pickup I had (not a BKP but very like a Holydiver) always sounded MUCH better at gig volumes.
I hope that helps.
Good luck
