I seem to have an issue with air getting into my fuel system if the truck sits, it will run rough for the first 10-20 seconds and then smooth out and run perfect.

Background:

Swapped the motor into an 84 K30 a few months ago and the truck ran and started perfectly for the first couple months. Then it began starting rough and running rough for the first bit, I've replaced the lift pump, the fuel heater o-ring, fuel filter, and now injectors (several were leaking between the body and nozzle and I had hoped that would fix it, doesn't seem to be the case but no complaints about the new injectors ). I can't find any leaks other than the injectors (that are now replaced), I've pressurized the tank and that didn't reveal any leaks.

Any hidden places air could be getting into the system?

 

Try plumbing in some sections of clear line before the lift pump, and on the return. That will let you know if it is air, and where it might be coming from.

Bubbles in the supply means it's somewhere between the tank and lift pump, and they will also be in the return.
bubbles in the return line only, means it's leaking between the lift pump and IP, or lift pump itself

 

I'll give that a shot