675 to 725 in 15 days is a solid trend, you're clearly doing more right than wrong here. The variable mix up on quant near the end is a fatigue tell more than a content gap, honestly. This test is less about whether you can do the math and more about whether you can tell which math to do, and that skill is the first thing to slip when you're tired. Worth checking whether it happens more in the last third of quant specifically.
The CR pattern you're describing, getting it right in your head but picking wrong between the last two, is the exact same thing I fought for months. It usually means you're evaluating the two survivors against each other instead of against the question stem. Go back and read the stem one more time, slower, before you choose between the final two. Sounds too simple, but it catches a surprising number of these.
For DI, the 5 minutes you lost on one question is the real story, not the accuracy. Try timed section practice where you cap yourself around 90 seconds and force a guess past that, even in practice. It trains the instinct to bail before it costs you the whole section.