My lower filler neck tube clamp leaks slowly drip by drip since a fuel pump change when I fill it with gas now - and it doesn't look like I can get on the clamp with tools from under the vehicle between the frame and the fuel tank. How do I approach this?

Try lowering the tank. That should give you more room to work.

I was afraid of that....fun fun.

Thread moved to Chevy mechanical and maintenance section.

Not sure on the stepside bed, but most Chevy pickup beds are super easy to remove. Often easier to remove the bed than drop the tank for fuel pump and fueling related issues. You might want to take a look at removing the bed, after removed super easy access to everything.

Dont do that just get a long flat tip screw driver and you can get to it there is also a clamp from the metal tube to rubber and that one can be reached from in between the bed side and frame rail..the other one is the rubber to tank