GMAT Strategy

Took my first mock test today after about 2-3 weeks of preparation and much procastination. Got a decent 650. I am targeting a score of about 720. And i have a month and half to go for my exam. I thought I could manage a score of 48 in quant, but was done in by my lack of keeping steady pace.

After reviewing today's mock, here are some areas I could use pointers on study strategies

1. I got 2-3 easy quant problems wrong and ended up spending too much time on some more regular problem type. Should I do all my studying / practice with a timer here on?

And are there any freely available resources that supplement the theory from Manhattan guide. I feel that the "In action" problems do not give adequate topic-wise practice.

2. Data sufficiency - Aargh!! Can never seem to wrap my head around it completely. Using the manhattan guides currently, but I dont feel they have enough practice questions here as well. Any alternate resource?

3. Verbal - Critical Reasoning - I usually do well in this problem type. Got about half of them wrong in the actual test.
How should I go about studying for Critical Reasoning? Do you suggest reading through the Manhattan Guide? I read the first chapter and I dropped it because I thought that the approaches described seemed too theoretic and time consuming. Any suggestions of an alternate resource or should I stick to the manhattan guide?

Any help would be much appreciated.

Thanks in advance!