I definitely want to keep my job. Will start telling managers I have too much BEFORE going in road.
Never, EVER falsify. As long as you're not screwing off, you have nothing to worry about. Don't make their problems your problems. While it's human nature to take care of those who take care of you -- there's a limit to it and Management will play you miles past the limit, but once the axe has to fall, it will be on your head.
Coding your packages as 8s only says "The courier was successful at attempting all stops assigned to them today, but it's the customers fault why they didnt get it cuz they weren't there." So the manager doesn't have to explain to the higher ups why you had dex3s, and it doesn't look like anything was wrong and you were dispatched perfectly.
You can only do so much. You can only go so fast on the road. You can only walk so fast at the stop. You can't control the traffic or the customers. What you need to do is make sure that you are being as efficient as you possibly can while following the rules. It doesn't matter if they give you 10 stops or 1000. Just be as efficient as you can be safely on road, communicate your status with dispatch, and there is NOTHING they can do.