How thick is the undersuit? I'd expect the material to weigh roughly what neoprene weighs, so if it's twice as thick I would expect it to be twice as buoyant, and therefore need twice the lead. What you're seeing where triple the lead is still insufficient, is a little surprising but not impossible if the undersuit is really thick.
I agree with @lexvil though -- at the end of the day, you need to to be able to sink at the start and to hold a shallow stop at the end. If you can't do that, slap on some more lead. Steel HP80's are already pretty negative, so the only other gear swap I can think of would be to switch the BCD for a steel backplate and wing, which take care of 6-8lbs or so. If you have buoyant fins, maybe negative fins would shave off another 2-4lbs, but it will have a large affect on your trim, so you'll want to dial in the lead and possible skills issues before trying that.
Just to be clear on the burping. Once the suit is completely on and sealed, you want to use your finger to break the neck seal, and then squat your whole body near the ground to squeeze air out. Stand up, stretch and wiggle around a bit, and then repeat. You shouldn't have any problems walking or anything, but it might be a little uncomfortable.
Try diving with the dump valve completely open throughout the surface swim and the entire dive. This will help you to maintain a minimal amount of gas in the suit. At the end of the dive, I sometimes have little red lines on my skin from where a wrinkle in the suit was pressing against my body -- if you aren't seeing anything like that, then IMHO your suit isn't completely empty. It shouldn't hurt at all, but a little stiffness in the joints is to be expected. By the way, some dump valves will leak when they are 100% open, so will need to be closed a few clicks -- my Apeks low-profile one has never leaked on me, so I keep it completely open every dive.
As for the leaks, what kind of seals do you have? If they are latex, you'll want to be using talcum powder before every dive. If they're neoprene, you may need to roll them in on themselves to make a proper seal. My suit has silicone seals, and I find that I need to be vary wary of hair growing on my neck where the seal meets my skin. Since I haven't had a proper haircut in over a year now (thx covid), I have gotten in the habit of shaving the little fuzzy hairs that grow on the nape of my neck, which has greatly reduced leakage from the neck seal -- maybe you need to do the same.
For some people, the tendons in their wrists pop out pretty high, and can break the wrist seals. If the space between your tendons make large peaks and valleys when you move your hand around, this might be your issue. Not sure what you can do about it since I've never had this problem, maybe others would have advice. But I believe you could eliminate it by switching to a ring-based dryglove system, like Kubi or Rolock. I use Kubi drygloves myself, and honestly haven't even been using the built-in silicone seals, since the ring system makes such a good seal.
