This is fine, not trying to take away from that, but as an example you get the Mule at 25, and unlock personal trucks at 45. That's a long time, especially with how bad the Mule is. It actually feels like a punishment rather than a proper sense of progression and by the time you unlock the personal vehicles you'll be moved on from Mule deliveries.
I'm not going to lie since starting with the Mule, I have almost basically stopped doing runs, it feels awful. I max out at 105, where as the Benson can easily hit 170-180. Again I know it's a truck and shouldn't be as fast as a car, but that's a lot of levels to suffer through, whereas it can be tuned to be in line with other trucks and it won't be a problem.