What could be causing my engine to be hard to start? on 2006 Chevrolet Silverado 1500

When the vehicle sits for several hours, the engine will crank normally, but won't start unless I press the accelerator to the floor and hold it. My mechanic diagnosed a bad fuel pump, but a new one didn't solve the problem. The check engine light does not come on. No codes either. Any ideas?

Asked by for the 2006 Chevrolet Silverado 1500
Have fuel pressure tested to see if pressure drops off quickly when the key is turned off possibly flooding engine. Then when the engine is cold to see if pressure is normal. TPS needs to be checked for proper readings at closed throttle.
I'll give it a try.