Oldtimer brings up a very good point
How are you verifying that the injectors are working properly?
You could measure the resistance of all 6. I don’t know your specs, but if they’re all the same, then at least you know it’s not open circuit. If it’s significantly lower or higher than the other 5, that could be a problem
A noid lite kit would let you know the injectors are being properly controlled
You could also perform an injector balance test, but that requires special tools. I’d check resistance first, though, as it should only require access to the connectors and a decent multimeter, which you hopefully already have
One more thing . . . #1 could be firing to ground. If so, this is typically due to bad plug wires. Read hole or tear in the sheathing. You can often hear the clicking, and sometimes even see the arcing. It helps if it’s dark outside