Перепад давления слишком высокий.

Because перепад usually takes a dependent noun answering чего? (of what?).

So:

• перепад = a difference / drop / fluctuation
• давления = of pressure

This is the normal pattern:

• перепад температуры = temperature difference / temperature fluctuation
• перепад высот = difference in elevation
• перепад напряжения = voltage drop

So перепад давления literally means pressure difference or pressure drop, depending on context.

Because it agrees with перепад, which is a masculine singular noun.

• перепад is masculine
• therefore the adjective is высокий

Compare:

• перепад высокий — masculine
• температура высокая — feminine
• напряжение высокое — neuter

Even though давления comes right before it, the adjective is describing перепад, not давление.

In Russian, the verb to be is normally omitted in the present tense.

So:

• Перепад давления слишком высокий. literally: Pressure difference too high. naturally: The pressure difference is too high.

This is completely normal Russian.

If you wanted past or future, then a form of быть would appear:

• Перепад давления был слишком высоким. = The pressure difference was too high.
• Перепад давления будет слишком высоким. = The pressure difference will be too high.

In technical contexts, перепад often means a difference, drop, or change between two points.

So перепад давления can mean:

• pressure difference
• pressure drop
• sometimes pressure differential

The exact English translation depends on the situation. In engineering, plumbing, medicine, and physics, перепад is a common technical word.

It is more specialized than a general word like разница.

Russian often uses высокий with measurements, levels, rates, and values where English may use high or sometimes large.

So высокий is very natural here:

• высокое давление = high pressure
• высокая температура = high temperature
• высокий уровень шума = high noise level
• высокий перепад давления = high pressure difference

You might also hear большой перепад давления, which means a large pressure difference. That is also possible, but высокий sounds very natural in technical language.

Слишком means too in the sense of more than is acceptable or desirable.

So:

• слишком высокий = too high
• слишком низкий = too low
• слишком большой = too big

It usually goes directly before the adjective or adverb it modifies:

• слишком высокий
• слишком быстро
• слишком дорого

In this sentence, it modifies высокий.

Yes. Russian word order is flexible, though different orders can sound more neutral, emphatic, or stylistically different.

Neutral statement:

• Перепад давления слишком высокий.

Other possible versions:

• Слишком высокий перепад давления.
  This sounds more like a noun phrase: too high a pressure difference.
• Перепад давления очень высокий.
  This means The pressure difference is very high, not necessarily too high.
• Слишком высоким является перепад давления.
  Grammatically possible, but much less natural in ordinary speech.

So the original version is a very normal way to say it.

A helpful stressed version is:

Перепа́д давле́ния сли́шком высо́кий.

Approximate pronunciation:

• перепа́д = peh-ree-PAHT
• давле́ния = dav-LYE-nee-ya
• сли́шком = SLEESH-kam
• высо́кий = vih-SOH-kee

A few notes:

• Final voiced consonants in Russian are often devoiced, so д at the end of перепад sounds closer to t.
• Unstressed о is reduced, so it does not sound like a clear English oh.

Sometimes, but not always.

• разница давления literally means difference in pressure
• перепад давления is more technical and often more idiomatic in engineering or scientific contexts

In many technical situations, перепад давления is the better choice. It can suggest a pressure difference between two points in a system, or a pressure drop across something like a valve, filter, or pipe section.

So for a learner, a good rule is:

• use разница for general difference
• use перепад for many technical expressions involving measured change or differential

Yes. Russian has no articles like a or the, so definiteness comes from context.

Перепад давления слишком высокий could be translated as:

• The pressure difference is too high
• A pressure difference is too high

But in real situations, English usually chooses the because the speaker normally means some specific pressure difference already being discussed or measured.

So the Russian sentence itself does not mark a/the; context does that.