1986 K10 stumbling issue

[capone550]

I have an 86 K10 with a brand new 350, 700r4, carb, distrubutor, fuel pump, etc...
Every now and then it will start stumbling on itself. I checked the fuel by cracking the fuel line to the carb and it was dry. If I switch tanks it will run good for a little while and then start stumbling again. I feel like it has to be either the switching valve or the hoses around the valve. Has anyone had this happen with the switching valve before? Could the lines be bad an collapsing? Could the valve not be totally switching inside? My plan is to bypass the valve and see if that takes care of the issue before I buy a new valve.

Thanks for any input!