>>> If something is speeding towards something else, I would personally say that it is not doing it slowly. That's the very nature of definition of speeding in this language. Instead of 'speeding', you could say 'approaching', or 'catching up to'. You also could simply remove the word 'slowly' and make no other changes. That would work.

>>> The disembark sentence is an special case, a construct as follows: Only when <action 1> can you <action 2>. Examples 'only when you pay bail can you leave jail'. Only when you eat your vegetables can you get dessert'. :)

>>> I haven't heard the word 'assail' be used in this context, but it works. It's clearer saying 'thoughts' (to me) and that could be a language-independent thing; more of a meaning thing. "assail" could be seen as poetic and that's why I'm hesitant to correct it.

Make sentence

1. It's a stuffy day.

2.The house is deserted so I'm a little bit scared.

3.The ship is speeding to a big liner slowly.

4. Only when the ship arrives at the destination can you disembark.

5. Some things thoughts always assail me so that i can't sleep well.

6. The sellers went to a great lengths to persuade me to buy the shirt.