I am having a bit of a problem trying to substitute the words which and for without changing too much the meaning/flow of the sentence. I have tried the thesaurus, synonyms, etc with no luck.
I achieved a strong 2:1 in X at Y University and excelled in modules studied during my final year, for many of which I received a First. This included a Financial Analysis and Control module for which I attained a strong First (72%) for a financial performance analysis of the Z Company.
"A First" (UK Grade) is like an "A" in the United States; I know it can be kind of bizarre when reading if you're not used to it.