Have you had a fitting on your new bike? At least with my own personal experience, if my saddle is too far foreward, I end up having to use my quads a bit too much--and that's not to my liking. Saddle height will also play a part in how much power you're able to generate. So, the difference in how you feel on each bike could be as straightforward as your saddle position. You could play around with that yourself, but if you really want a more systematic approach that will likely get you happily rolling sooner, then meet with a professional fitter. Catrin and I have both used--with great success--the fitter at Nebo Ridge. It's well worth the money in my experience. It matters not that you didn't buy the bike there, and the fee you pay is good for the life of the bike in case you need further adjustments.