Copy and paste your whole book into a new file.
Then cut the page count by half. Delete the fat, leave in only what's absolutely necessary to the story. Be merciless.
Then go over your original file and compare.
Another thing to try is highlight only the most necessary dialogue in yellow, plot points in green, only the truly necessary descriptive in red. You may find a lot of white space of stuff that isn't needed.
And finally--read really good mystery writers to figure out how THEY did the pacing in their books. Classic stuff by Agatha Christie--who was an expert at plotting/pacing--will totally help you.
Reading plays will also help, along with TV scripts, which tell a whole story within 40 minutes. Read a book on script writing, which tells how those 40 minute stories are paced. They have to fit that story in between commercial breaks.
Law and Order is a good series to study for pacing. The first half is about the crime and getting the badguy, the last half is the court time. They cover a LOT of ground! Somewhere there will be transcriptions of the scripts up on line.
Good luck!
