As always, it's dependent on location, situation, & how much reach around you are willing to do in managements favor.
Good luck if they don't decide to like you for whatever reason - at least with UPS I have the contract bible to shove in their face when management gets too invasive.
Never worked private fleet, but did pull as dedicated contractor at Olney, Lewiston, Pottsville, & Shelbyville years ago - most WM drivers were very happy with their job.
I never had a problem with management or saw them out of line with any driver interactions - got to wait for loads with several senior WM drivers on the regular & they had a down to earth view of not sucking the company Kool aid while still being appreciative of the job.
One older dude had already retired 30yrs from UPS Chicago & said Walmart was miles better to work for.