It takes time to adapt to a dramatically different position. Usually a couple weeks. The metabolic adaptations that allow you to make that power are still there, but you lack some specific muscle strength to utilize it in that position. Same way increasing FTP on the bike can translate to the run and swim, but you have to develop those muscles to use those same metabolic adaptations. Some are muscle specific, some are more systemic.
At some point there are some mechanical limitations of the more aero and forward tri position. But it's almost always a good trade for overall speed. But it sounds like your fit may be so poor that you are getting the worst of both.
No way to make any suggestions without pictures. But as a general rule, most people need to visualize the position are "rolling forward" not getting lower. The front end gets low because you rotate your entire position relative to the bottom bracket. You slide forward, arms get lower but not necessarily more stretched out. The limiting factor of the position becomes neck flexibility to see where your going and hip angle. Hip angle is mitigated with shorter cranks. But if your rotating, the relative hip angle doesn't change much. You do however place more weight on your shoulders and require more core strength to leverage power. This becomes a limiter for some, as well as neck flexibility.
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