The 'trick' is not to count, and just 'feel' it.
IMO this is really crucial.
Raindrops, are you able to hear each part (while playing) or does one take over your attention? I've found that I do better when I can hear both parts, and I can tell I'm off when I can only really hear one part (usually when this happens, I can hear the RH but not the LH).
Also, not specific to 3:2, but how is your fingering? Have you made sure that you can play each part HS at much more than your desired tempo? If you can't, then you might consider doing a little bit (but not too much) of HS practice. If after that, you find that you still can't really speed up HS, then it might be a good idea to see if you need to reconsider the fingering you're using.
If you find that you *can* play each part HS at a good tempo, then go back to HT and work towards feeling it. Here's what I would recommend.
Play the 3:2 section HT at the fastest tempo that you can currently play and still have each part correct. Now play HS, just a little bit faster than that tempo (no metronomes, no counting).
Now go back to HT at that slightly faster tempo. Don't stop just because you're out of sync or not doing one part just right. Try to push through it.
Oh BTW how many measures does this go for? I'm thinking of a piece I play with a 3:2 section that goes on for 16 measures, if yours isn't this long, my method might not work. But if you can play it as a loop it might. anyway...
Now go back to HS, same tempo, and play each part listening very closely so you know what you want to be hearing.
Now HT again, at the fastest tempo you can manage while still playing it correctly.
Now HS again, slightly faster.
Now HT, again try to play at the faster tempo. If you're out of sync, just push through it. See if you can get one hand, say the RH, correct even if the other, LH is off. Now see if you can switch, so you focus on getting the LH correct even if the other is off.
The point is to go back and forth between HT at the tempo you can manage, HS at a faster tempo, then try that tempo HT and keep going back and forth, ratcheting up the tempo w/out the metronome, but by having a slightly sped-up HS practice as the way you get progressively faster.
If you can play it HT correctly, even if it's slow, you'll eventually be able to play it faster correctly, HT. I just think you probably need to knock your brain out of the slower tempo, and HS is a good way to do that. Also, not focusing on playing perfectly at first. Because what you want is to
feel playing 3:2 at a faster tempo, so it doesn't matter if you're playing it correctly at this point.
I don't know if this explanation is easy to follow but that's how I've gotten myself able to play 3:2. Good luck to you!!