The following sentence illustrate several kinds of nonparallel constuction. Rewrite the sentence to achieve parallelism.

If you insist on reading the Old Testament all the way through and to do the same with the New Testament, you are in for some big surprises.

Would you write it like: If you insist on reading the Old Testament all the way through and doing the same with the New Testament, you are in for some big surpises.
or..........
If you insist on reading the Old and New Testaments all the way through, you are in for some big surprises.

Reading the Old Testament all the way thru, then reading the New Testament all the way thru, you are in for some big surprises.

Your second approach is excellent.