You need to spend less time pouring over your sermon.
Yes, get the text down. Put it in your blood, your soul. Memorize it. Read it over and again. Get a few commentaries. Be critical of them.
But when it comes down to it, the actual sermon prep shouldn’t take more than 4-6 hours. Maybe a couple more for writing, outlining, and running it once through.
The rest of your time is spent preparing to preach. That’s more like 25 hours a week, including:
Reading books. Read theology (which I consider, broadly, anything to do with the study of God). This keeps your preaching fresh, wise, and strong. It gives you illustrations.
Read fiction. This teaches you how to read the 90% of the Bible which is narrative. It teaches expression, imagination. It gives illustrations.
Read biographies. These inspire you. They teach you human nature. They give illustrations.
Private Prayer and Study of the Word. At least an hour a day, if you’re a full-time pastor. You have to stoke those fires. You have to come to the pulpit aflame. You can’t walk up there on the crutches of a mild devotional life and 20 hours of textual gymnastics under your belt. Get yourself to know God. Bring yourself before Him. Let Him pour out to you. Your feet should be smoking by Sunday. It’ll give you illustrations.
Keeping up with culture. That means: reading the newspaper. Keeping up with blogs and trends. Watching the TV shows and movies your congregants are watching. Watch their sports gods and goddesses. This will teach you your people’s religion. It will teach you how to catechize them (you’ll learn their questions). It’ll give you illustrations.
The reason outlining and writing a sermon come quickly to me is this: I always have ready application and illustration from the 25 hours a week I’ve spent OUTSIDE my text.
So put in your 4-6 hours to study the text. Memorize it. Soak in it. Write it out. Run it through.
But come Sunday, don’t be content with a ready sermon. Come as a ready preacher.