Tweaking the truck program here and there to get better surface finishes, and I'm actually super happy with one little change that greatly improved the bottom face!
Since this model truck is cut from a block of aluminum in one operation, there's a very long and slow process of cutting it off the base fixture that requires super slow feedrate and RPMs to avoid marring the surface. In the design, the car has a completely flat bottom with only z-height changes contouring the car's outline. The problem with this is that we don't have a tool with a long flute length to take it all at one pass, so it has to be taken at several steps with a short and stubby tool. This causes the side of the endmill without any teeth to rub against the side of the part, leaving a burnt-like surface appearance. Thankfully it doesn't affect the car in any way; it just leaves a pretty poor finish.
My setup currently consists of removing all but a 1/4" strip of aluminum in the center of the truck, at which point the machine pauses in front of the doors for me to add the clamp fixture. Once I properly secure the truck onto the remaining stock, the machine runs a stubby long-reach tool and takes very small stepdowns until it cuts the truck off the base.
My boss suggested having the long-reach tool not contour the bottom of the part, but a few thou (0.0004") away from the side, so that the shank of the tool (the part without cutting teeth) wouldn't rub against the walls. This actually worked amazingly well, and I got a fantastic finish! I also made some small changes to the corners where previously I would get tool chatter as it runs into a corner. For this, I only had to add a slight radius to those sharp corners so the tool wouldn't have to dwell but could smoothly run through without pausing. Though slight changes, it makes a huge difference in the overall quality.
In the video, the first car I show is the old version where you can see the surface marring and chatter marks; then the second truck is with the new system of having the tool away from the sidewall and smooth corners.