Using asteroseismology, we analyse late subgiants and early red giants with long cadence data from Kepler. These two phases are key for studying the first dredge-up, when deep convection transports nuclear-processed material to the stellar surface. Asteroseismology constrains stellar masses and radii through the global seismic parameters νmax (scaling with surface gravity) and ∆ν (scaling with mean density). However, many stars in this evolutionary stage were observed with Kepler's long-cadence mode (29.4-minutes sampling), which limits the highest recoverable oscillation frequency to the Nyquist frequency of ~283 µHz. Modes with frequencies above this threshold are aliased i.e. they appear mirrored in the power spectrum making them challenging to interpret. To overcome this, we developed a method within our seismic data analysis code PyA2Z to detect and characterize these super-Nyquist oscillators. Applied to ~2000 Kepler targets, our method yielded 282 super-Nyquist and 170 close-to-Nyquist stars, spanning 0.8-1.6 M☉. In addition, we measured the global seismic parameters of 867 stars with νmax below the Nyquist frequency, which, together with the super- and close-to-Nyquist detections, provide a sample of ~1300 stars that allows us to probe the first dredge-up. By combining seismic inferences with APOGEE spectroscopy, Gaia photometry, and stellar models, we derived precise masses, radii, and ages for those stars. Our analysis shows that while the timing of the first dredge-up agrees with stellar models, its magnitude does not - indicating potential shortcomings in current modeling prescriptions or systematic biases in the seismic and spectroscopic calibrations.