I have a leak only when filling up
It's in the Fill Tube Not sure where as in in upper or lower section but I know it's above the anti siphon ball

Would there be any issues with just replacing everything with rubber fuel rated tube?

 

I had to replace the filler line on my '95 when I did the fuel pump; only tube I could find was at Checker (now O'Reilly's) and had to buy 4 feet of it. It is rubber with a steel wire wound into it...required a hacksaw to cut it. Had no problems for couple of years afterwards, then sold the vehicle. I think I still have three feet of the tube sitting in my garage as I bought another Blazer and wanted to be ready and the tube was not cheap!

The filler was rubber on my '95....would think it would be the same on your '97.

 

Filler and vent line are steel with rubber couplers in the 97

I'm mostly wondering about the affect of the rubber line and the evap system test

 

After thinking about this more.....I believe that the '95 also was a combination of steel and rubber....I just replaced the last section of rubber that goes to the fuel tank.

You could probably remove the filler tube completely from the vehicle and then throughly inspect if for leaks. I would not think the evap system test would care if the line was rubber or steel/rubber as long as there were no leaks.

Can you tell what section of the line is leaking when filling the tank?