I grew up with Wilbur Shaw, Jr (we were born the same year) and I knew his father as well as any 9 year old can know a friends parent. In October of 1954, his father (3 time winner of Indy 500 and was President of the IMS) was flying back from the Chrysler Proving grounds (in the Detroit area as I vaguely remember) along with the Speedway artist that had drawn all the winners to that date and Ray Grimes, a Cessna demo pilot, in a Cessna 195.
They were pushing to get home for Wilbur's birthday. They got into icing conditions and fell out of the sky crashing into a field in Northern Indiana.
So, yes, Chrysler has had access to proving grounds for a long time. In fact the IMS was used by Firestone to test tire designs as my father participated in those tests in open wheeled race cars of the 30s. The riding mechanic's seat held the observer who'd watched the right rear tire and when a bulge appeared, he elbow the driver. However much the car was able to slow down before the tire blew out determined the rest of Mr Toad's wild ride.
The build quality issues in American vehicles finally started improving after the foreigners opened plants in the USA and put our domestic cars to shame using the same USA labor pool the Big 3 utilized.
I see truck "mules" of all sizes all the time in the Apache Junction, Arizona area testing the Allison transmissions.