Been here done that. Was never satisfied till I swapped to a road bike.
Your bike is geared for off road. Whats the crank? 26/34/42? Road you likely want something along the lines of 28/36/48 if there is hills. Thats a common Touring gear set.

The lack of drops doesn't let you tuck if you are fighting a head wind. You are pushing about 6-8 extra pounds and those that say weight doesn't matter are flat landers, when you are going up hill it does matter especially if the weight is in the wheels. The lighter the wheel combo the easier it is to spin up and keep spun up.

With the distance you travel I'd seriously start looking for a touring bike. Depending on your height you might look at buying a Long Haul trucker. The smaller sizes run 26 inch wheels and you could throw your drive train and wheels on it.

Looked up your tires...lots of reviews say they feel slow.

OMG! they weigh 1k!!! No wonder you feel like you are pedding in sand.

Try a set of panaracer Pasela TG's. They weigh less than half of what you have on there now. Well regarded for flat prevention. Often find sales on them around $20.