I would start by finding the software leaders in your vertical markets (vertical markets are how the software vendors classify customers). In my opinion, it is better to select a system that is very strong in one of the areas of your business (Routing or Project Management, go with the most critical piece unless you find a solution that does both well) versus a software package that is average for both. From what you posted above, it sounds like you may be a hybrid of the manufacturing, food and beverage, and the maintenance/service verticals. There are research companies you can buy reports from (Gartner, Aberdeen Group) that will rank systems by vertical and provide white papers to get you started. Once you have an idea of the leaders in each vertical, hit their webpages and sign up for a demonstration.
After each software demo, be sure to get customer references you can speak with, or better yet, customers in your area you can visit to see the system in use. You have to remember that it is unlikely that any one system will meet all your needs. The real key is to satisfy the majority of them and then understand where you need workarounds or 3rd party add ons (another key to research and ask about: 3rd party products).
Lastly - I know Dynamics GP has a well developed network of 3rd party soltuions providers, make sure you start with the devil you know versus the devil you don't ;)
Remember to take your time and you will do very well.
Hope this helps and best of luck