Your problem, as far as I can understand is not with pacing. Pacing comes naturally when you have developed a natural streak at solving problems faster without actually trying to be quick. I tend to think that you need to work diligently on the following aspects.
1) Read the question carefully, develop the habit of reading the question only once, may be a little slowly, with pausing, but surely understanding what exactly is given and what exactly is asked. You must develop the technique of segregating the data and information appropriately, without possibility of any mistake.
2) When you know what is given, and what is asked, you must then naturally think of how to get there. Most quant problems follow patterns. There are numerous problems on this forum for each question type. Word problems, DS questions, number theory, probability, permutations and combinations, statistics, exponents and fractions, geometry, coordinate geometry, algebra........etc etc, sustained practise alone can help you quickly figure out the right method, right procedure of approaching to the solution for any problem. The same applies for verbal as well. Verbal too, follows specific rules. The ability to apply the right rule blindly without much guidance, and without your conscious effort should come naturally. This can be gained only with more and more practise.
3) Practise reading. Read a lot, read anything and everything. And when you read, don't just read. Understand the gist, read critically, comprehend seriously, digest the data, facts and information, analyze the context and content, identify the structure, style and pattern of the content at hand. This practise is to improve sustained focus. Concentrating for 4 hours at a stretch is a pretty tough job.
4) Solve questions, maintain an error log
. It will constantly keep track of your fundamentals and basics and helps you fall back when you are facing a troubling issue at solving any tough questions. No questions are as such tough or easy, it all depends on your state of mind at any given moment. But GMAT questions, all follow specific patterns. The quicker you can identify the pattern, the easier the question becomes and the faster you can answer it.
5) Take full-length timed tests regularly. Most important aspect of all is the ability to focus for longer hours without feeling/getting tired. You need to train your concentration in such a way that despite getting tired, you should still suck up energy from the remotest body parts for use by your brain.
6) Stay healthy, stay positive, GMAT is not the end, it is just a part of the journey.