I own a 23", so things might not scale directly, you probably have way more mass to heat up than I do. So, I'm not surprised it's taking a bit of extra time to reach your target temps.
One cardinal rule of KK cooking - Don't chase the temperature! Learn your top vent setting for a given temperature (1-2 full turns is way too much, btw) and stick to it. It's OK to open the top vent wider at the beginning when you're lighting the grill and it's coming up to temp. But, set the top vent to its correct setting when you get about 50F below target, or you will overshoot and it's a pain to get it back down once the KK is heat soaked.
I'm discovering that the size of the charcoal does matter (Pun Intended). Been using Fogo and Quebracho lately and they have very large pieces of lump. If I use too many in the basket, my time to temp is a lot slower than if I use mostly medium sized pieces. YMMV