Leveling is American spelling. Levelling is British spelling. Levelin' is how I say it.
I've had a similar experience to you. I'm not sure Replay Gain and/or DSP is the solution to a low-volume laptop.
But it's asking a lot to have Replay Gain manage a huge db range. To get this under control, I made a view sorted by the Replay Gain value. I could immediately see a few tracks that were way out of the normal range, some too loud, some too soft. Depending on which of these were in the current playlist, the average volume seen by MC was shifted abnormally. The solution was to fix the extreme recordings, essentially normalizing the deviants.
Using an audio editor, I adjusted the level of each of these to be more reasonable (I kept the originals and adjust copies). Then I put the corrected tracks into MC. Playback with Replay Gain active has worked much better ever since.
That said, I also use a DSP audio compressor from AudioProc.ca, because I like radio station type sound. (I wrote an article about this...) The combination of fixing bad tracks, then using Reply Gain and AudioProc (which also does multi-band processing to even out the sound of very different recordings) for playback, gives me a very consistent, smooth sound.