twodownzero -
Some corrections to your posts you have made:
1. Class 2 and 3 trucks are very similar in build between each other and can even be ordered in down rated GVWR to allow less expensive commercial licensing cost even though they are identical trucks to the higher rated ones. The F450 pickup is actually a beefed up version of the F350 and can also lumped into this group. Many parts are identical or interchangeable in these two classes and you even order a Class 2 truck that has higher ratings than the Class 3 if you choose your options carefully.
2. Class 4 and 5 trucks are chassis cabs which share body and some power trains with the lower class pickup trucks. Much less of the chassis, suspension and axles cross between the pickup and chassis cab lines. Between Class 4 and 5 trucks much of the parts are interchangeable like they are between Class 2 and 3.
3. The chassis cab models are not limited to 4.88 gearing. Gas engines can have 4.30 or 4.44 gearing while diesels are also offered in 4.10. Although power trains are similar to Class 2 and 3 pickups, they are detuned to be able run at maximum output of longer duty cycles at heavier loads than the lighter pickups.