There we are, coasting along just fine. Our playing is good, and so is life. Suddenly a few nasty passages begin to become troublesome and demand our attention. Simply ignoring them has failed to produce any improvement, and muscling our way through them isn't working. Neither does repetition - something about expecting a different result without ever changing anything? Those gnarly intervals seem set on remaining obstinate and refuse to be conquered. What is a trumpeter to do (besides yelling and throwing things)?
Here are a few suggestions that always yield results in the shortest amount of time. They are not new or amazing over-night cures, just remedies that work, but require consistent attention. In addition to mind-over-matter brute strength, which does have its place, you can get used to making these procedures a regular part of your routine as well.
The last thing we usually try is PLAYING VERY SLOWLY, I mean really slow. Try half tempo, so that you can totally focus and hear each note. Usually the tongue has become brutal, sluggy or pecky. Over-articulating is often the problem. We resort to using a sledge hammer to kill ants. The sledge hammer has its place but should not be over-used. When playing painstakingly slow, we immediately notice the lack of quality and center of the notes.
That leads to the next item: CLEANING UP THE SOUND. Sound quality generally suffers with speed. Play each note slowly with your best tone. No junk notes allowed. You ought to be able to sound just as good as your heros, if you play slow enough. So we've got slow accuracy, and now greatly improved sound.
Next is mouthpiece BUZZING. This perhaps should be the first resort. Insist on perfect intonation with your buzz. Very few seem to avoid modulating when buzzing even the shortest passage. Sit beside the piano while you plunk out the notes, checking your buzz for clarity and exact pitch. So now we have slow motion, high quality and a nice-sounding buzz.
Is anyone still there? Another item we all hate, but it works - and that is SINGING. Whether you have a good singing voice or not, it doesn't matter. Sing the passage in tune and in rhythm. As this improves, it will help your concentration when you return to actual playing. We easily get careless about slotting notes. Hence, pitch, quality and volume are hampered.
In short, if you can't play it, SLOW IT DOWN, listen for SOUND QUALITY, BUZZ IT, and SING IT. Take your time. Impatience is the root of the problem.