There is some overlap in how you need to think about both. For example, really understanding inferences within critical reasoning will also help you in inference questions in reading comprehension. That said, you should still practice both and keep a detailed
error log for both -- there's no substitute for practicing reading comprehension strategies on reading comprehension. The timing in how long it should take you to read and the strategy of how you read is different for the two. On critical reasoning, it really helps to read the argument very carefully so that you don't have to read it multiple times. But in reading comprehension, close reading of the passage itself is going to be time consuming and so reading the passage itself requires a different strategy.