TA struggling with how much time grading takes
One thing I might do in your shoes is to grade all the answers to the problems one at a time.

That is grade problem 1 on the assignment for all 74 students, then grade problem 2, and then add up the scores for the seven problems at the end.

That way, you can "prepare" for one problem, grade it on an "assembly line," and then forget about it after you go on to the next problem.