1987 TBI R10 quit running on left tank

[87ChevyR10]

Any insight is appreciated!!!

I started my truck the other day and it ran as usual for about 5 minutes then quit. I tried to restart it and it will start with some pressure on the throttle but sputters out and doesn't run as it should. When I switch to the right side tank the truck runs fine. I tried again yesterday and I still have the same problem. I do hear the pumps running before initial startup.

Where should I start? I read that it could be several things but I think it is either the pump is not building enough pressure (bad), the rubber hose in the tank is cracked, or the selector could be bad.

It does look like the selector has been replaced by the PO but I have no knowledge of when and I have owned the truck for 3 years with no prior related issues before.