しっかりと大学の課程を終えました。

English Translation

I completed the university course comfortably.

The と is unnecessary, right?

@ericaw
No. Both しっかりと and しっかり work to modify a verb. For example,

一度開封した袋は、しっかりと口を閉じましょう。= Once you open a package, you need to tie it closed firmly.

首相は野党の主張にもしっかりと耳を傾けるべきだ。= The Prime Minister should also sincerely listen to the criticisms from the opposition parties.

You can omit と from these sentences, but しっかりと sounds very natural.

Other example phrases in the same pattern are:

  • ゆっくりと/ゆっくり = slowly

  • きっぱりと/きっぱり = explicitly/with no second thought or regret (e.g. to turndown an offer or deny an allegation)

  • ざっくりと/ざっくり = roughly speaking/roughly estimating

  • じっくりと/じっくり = thoroughly with caution (e.g. to think or execute)

  • ハキハキと/ハキハキ = briskly (e.g. to answer)

By the way, the collocation of the original Japanese sentence is unnatural. We don’t say しっかりと終える (completely/firmly finish) when we refer to an educational course. Moreover, しっかり(と) doesn’t mean “comfortably” at all.
My alternative translations are:

大学の課程を修了するのは楽勝だった。(pron. 大学のかていをしゅうりょうするのはらくしょうだった)

私は楽々と大学課程を修了できた。(pron. らくらくと)