Is it possible to tell if injectors are stock without removing them?

I've yet to run a full tank of fuel through the system, as I'm working on minor issues and want to replace fuel tank sending unit (gauge wacked out).

While learning the characteristics of the truck, I've mashed throttle going thru the gears up to 2500 - 3000 to see how it runs. (hyper-miler by nature tho). Truck smokes heavily above 2000 rpm.

The only aftermarket item visible is a banks exhaust brake, which is currently disconnected. Unknown why.