Fuel issue with Cub Cadet Commercial Z turn...

I've been happy with my slightly used 48" Commercial Z turn with the steering wheel I bought a couple years ago- really cut my mowing time in half. Other than a deck belt tensioner spring coming loose, which was easily fixed once I figured out what had happen- a pin came out of the fastening clip, no problems.

But recently, when I use the left side fuel tank, it'll run for a while, then die. It's a lack of fuel issue. Works fine on the right side tank. I tried loosening the cap, thinking maybe it was not venting, but that's not it. Both tanks are fairly full, same new gas in each. When I first start it, cold, it'll run maybe 15 minutes on the left tank before dying. Restart on the right tank, runs fine. Switch to the left tank, runs for maybe 5-10 minutes, then dies again. Before I start investigating the fuel pickup, the lines and so forth, thought I'd ask if anyone has any experience with this problem? It'll give service with just the right tank, but not ideal. Thanks.

Most likely debris in the left tank blocking the outlet or built up at the switch.
A lot of tanks get fitted without the casting flash in the outlet being cleaned off .
This will catch any debris ( grass clippings etc ) and eventually cause a plug.

You may be right on. Yesterday, the left tank worked just fine. When the fuel gets lower, I will investigate. Thanks.

Cheap & nasty test is when the mower stops, remove the filler cap then remove the fuel line & blow backwards down it.
If it feel really hard to blow & the mower runs fine for a while after then that confirms you have a blockage.

Once cleaned out try to run from each tank more often
People tand to run two tank mowers like one is the main tank & the other a reserve.
Thus the left ( usually is the left ) rarely gets fully drained and debris accumulates in the bottom.