If it's important for you to go faster and/or longer, you have to practice (or "train") going faster and/or longer. There will always be somebody passing you no matter what, but you can optimize the performance you get from the effort you put in by good, efficient positioning on the bike. There is no substitute for having the saddle in the right place (high enough and not too extreme fore-and-aft), and your upper body leaning forward enough (this dramatically improves performance because it uses all of the muscles you have available for pedalling).

There's no doubt that having to accelerate and push big tires with heavy tread is going to slow you down compared to those who aren't.