454 hesitates when cold
 

I have a 1996 chevy 454 P series engine in my RV. It was rebuilt and ran perfectly for about 2000 miles. Now it hesitates when cold. Runs fine after about 10 minutes when it gets warm.

All fuel injectors were replaced and the computer shows NO trouble codes.
Technican says that he thinks the fuel pump may be the culprit because he sees air bubbles in the fuel line. I don't know what the pressure is cold or hot.

When cold it idles slower than I think it should. Starts immediately every time. seems to be a miss at the tail pipe when cold but clears up when warm.

Could it be some sensor or vacuum line keeping the computer from keeping an increased idle until warm?

I would like to investigate some easier possibilities before I remove the fuel tank and replace the fuel pump.

Thank you in advance.