It's day #1 on your orchestra gig. Life is good until you open the folder. There you are faced for the first time with Berlioz' Roman Carnival Overture with the cornet part in A. Next, you have Tchaikowsky's Romeo and Juliet Overture with the trumpet part in E and F. On the second half is Ein Heldenleben, and you've got the E flat part! Any of these transpositions at first sight in a rehearsal could cause some degree of panic not unlike drilling with no Novocaine. You just don't want to be there, so now is the time to do something about it well before you get the gig.
The remedy for this situation is a good skill in basic transposition. You may think of this as root canal work because it's embarrassing to sound like a beginner when having to transpose something. It's like trying to run with your feet in concrete blocks. But some daily pain in the practice room is far better than humiliation on stage.
So let's keep a Sachse or Caffarelli transposition book on your stand for daily use. If this is your first exposure to this unpleasantness, here are the assignments: Transpose to A, C, D, E flat, E natural and F. Get familiar with these and then you can attack A flat, D flat, G, etc. Begin with easy stuff to gain confidence. How about a key a week?
Remember, you can do most of the grunt work without your horn! The issue is speed from page to brain to fingers, so you can save your chops for now. Try to like this, it is possible. It takes time but it does get easier. Transposition is a skill that is quite doable no matter how you play. Do it and conquer laziness! Not transposing well is a character weakness, not a disability. Daily drills will keep you from the drill.