88 crew 454 tbi fuel tank selector issue

[dieseltech619]

I have owned this truck since November and drive it pretty regularly, i am still chasing down gremlins with it but i have found a new one, my truck is stuck on the left tank. I fuel up atleast once a week amd always fuel the opposite tank to the one im currently running. This morning i fueled up on my way to work and flipped the switch while at speed going down the road and the truck died , i flipped back to the left and it came back to life. I tried this a few more times at different road and engine speeds all the same results. Since i have owned this truck it has had a slight stumble while switch tanks in either direction while going down the road and has always stalled while switching at an idle. I started checking simple stuff fuses and the connections to the switch all seem good but i did notice when i switch tanks the gauge is not changing with the switch it stays at the left reading. Any insight on this would be much appreciated .... thank you in advance