Dracula, it is the same principle for anyone who follows the methods in driving: you slow down to maintain your cushion. Methods change, but the principle is the same. A package car ain't a feeder, but it isn't a regular vehicle, neither. Neither is an air-braked equipped vehicle; I've driven both. You adjust, then you move on. I'd like to ask you if you understand what, "going with the flow of traffic" means, if you seriously just typed "you cannot maintain a space cushion going with the flow"; if everyone is doing the same speed, once you have initially set up your space cushion it will not change, save for minor adjustments. Of course everyone doesn't go the same speed, but just as in a package car, you let up off gas (maybe give trucks a little brake, since they need more to slow down), let cushion re-establish itself, and continue on. Only problem is when you are overtaking vehicles, which means you are going too fast, or not with the flow.
I can't listen to anyone who seriously touts the highway speed limit as an issue of safety, since the facts are out there to know better. Also knowing how UPS discipline works, a driver isn't going to get fired for going 54 mph on one bright blue sunny day; he is going to be told repeatedly he needs to speed up, and it is no where near the same as telling someone to run across a multi-lane highway, or jump off a bridge, or ride with a doughnut tire at speeds over 55mph. Come to the aid of this "brother" if you want, but sometimes you gotta know when to call family out.
And just because someone drives over the limit doesn't mean they must be drafting off you; you can drive over the limit using the habits, as millions of truck drivers do, which is why those who fight when mgmt says speed up can get in hot water.