On PS problems, you have no choice - you need to solve them completely.
You need a time saver strategy on DS - and it is you don't need to solve DS problems completely. Once you get a vague idea of the right choice, move on. Don't double check - in your case you don't have time for that. Treat the problems you've already answered as scored, don't linger, don't get previous question paramoia get to you.
Also - practice GMAT math problems a lot