Teeth on the front chainring divided by teeth on the rear cog. 52/20 = 2.6.

It sounds like your issue is that the gear is too low, where you're turning the cranks quickly and having a hard time keeping resistance on the pedals. For this, you want a higher ratio, either a bigger chainring or a smaller rear cog. A 52T chainring is already pretty big; you could make a large difference by using a cog a few teeth smaller in back.

For instance, if you switch to a 17-tooth cog, you'd have 52/17 = ~3.06, which is about 18% higher than your current gear. So you'd be going 18% faster for a given pedaling cadence.