The detail level I provided is the "major" classification division. At "minor", trucking is only the 12th largest employment classification. There's a breakdown to fine detail (and I'm not sure what classification system is used) in which "truck driver" is the most numerous single entry, but that's almost entirely an ontological artefact:
truck driving doesn't have a bunch of fine subdivisions. Contrast the employment classifications for "teacher", which has something like 50 distinct sub-categories.
1 41-2000 Retail Sales Workers 8791750 62.619
2 35-3000 Food and Beverage Serving Workers 7355090 52.387
3 43-4000 Information and Record Clerks 5630810 40.105
4 29-1000 Health Diagnosing and Treating Practitioners 5143640 36.636
5 13-1000 Business Operations Specialists 4629810 32.976
6 53-7000 Material Moving Workers 4580950 32.628
7 47-2000 Construction Trades Workers 4216890 30.035
8 25-2000 Preschool, Primary, Secondary, and Special Education School 4133490 29.441
9 43-5000 Material Recording, Scheduling, Dispatching, and Distributi 4101520 29.213
10 15-1100 Computer Occupations 3997370 28.471
11 43-9000 Other Office and Administrative Support Workers 3940510 28.066
12 53-3000 Motor Vehicle Operators 3934070 28.020
13 35-2000 Cooks and Food Preparation Workers 3190940 22.728
14 37-2000 Building Cleaning and Pest Control Workers 3174220 22.608
15 43-3000 Financial Clerks 3133030 22.315
16 29-2000 Health Technologists and Technicians 3018820 21.502
17 49-9000 Other Installation, Maintenance, and Repair Occupations 2836540 20.203
18 39-9000 Other Personal Care and Service Workers 2820750 20.091
19 13-2000 Financial Specialists 2651370 18.884
20 51-9000 Other Production Occupations 2582350 18.393
I've looked at this before ... in June of 2015 ... and the result was very nearly the same. From then:
https://www.reddit.com/r/dredmorbius/comments/3832wx/occupat...
And yes, I have not broken this down by state, let me see if I can find that data. It's also worth noting that the NPR article uses Census classifications, which may differ from those I've listed (though Census is one of the participants in the NAICS classification, itself shared between Mexico, the US, and Canada).
NPR are ... unclear in the extreme ... as what specific data fields and employment classifications they are using. Given the NAICS categories above, multiple states would have to show peak employment in one of the listed categories above "Motor Vehicle Operators". And yet, none do.