Also, the OP sort of indicated they might not have been in the lowest gear ratio.
I think the gearing is OK, I guess. It's not like I ever ran out of gear. I could keep spinning at a decent rate, but I was going so slowly that I was wobbling all over the place.
So what also might need to be cleared up is what the OP thinks is a decent rate to spin. I consider my legs to be weak, so I compensate by spinning a high cadence and sitting for most all my climbs. My climbing cadence is often faster than my cruising cadence. So typically 90 rpm or faster. As another pointed out, at 4.5 mph someone with typical road bike gearing isn't spinning a very high cadence. In a 36-30 the cadence would be less than 50. And if there was a lower gear that could be shifted to, then for shame, because as also pointed out by another a faster cadence just helps with balance. On our MUP, I have no issue following walkers at 3.0 mph until they clear the oncoming traffic and I can pass.
As well the actual grade and ascent distance would be nice to give us some perspective as to whether it was what others might consider a hard climb or just a long climb requiring some constant grinding away. The OP has been riding for a while. So unless they only ride irregularly and just one day a week or less, they should be in acceptable riding shape.