Nobody told me when I bought my road bike that the tire air pressure should be checked before each ride. Hope the OP is doing that.

I just switched from all-weather commuter 700x25 to a faster 700x23 tire just on the rear wheel. My avg speed went up over 1/2 mph over my usual loop 25 mile course. I didn't get faster on the very steep uphills (4mph) or on the steep downhills (33mph), it was everything in between. The bike just feels more responsive and rolls easier. I'll be changing out the front tire within 2 weeks before a fun "race".

I'll put the commuter tires back on when I find myself riding solo in the dark again - they are almost flat proof and a little more comfortable on rough pavement. I've worn out 3 sets of these armadillos without a single puncture, ~7K miles.