v6 to lq9 swap fuel issues

Did a v6 to lq9 swap in my 2000 silverado. Engine is in and running, but sometimes you have to crank on it for a little bit, and sometimes it start first crank. It still has v6 fuel pump fyi, not sure if their a psi difference. But once it starts it running ok until you quickly smash gas then it trys to stall out almost like flooding it. Then another issue is when its cranking trying to start i see sometimes gas spitting out passenger side exhaust manifold....thoughts???? O2 sensors arent plugged in behind exhaust manifold so its in lag mode with service engine light on.

Check fuel pressure while driving. Let us know. Should be 55psi or more.
Turn key off and observe. Fp should hold.
If u cycle the key several times and then crank and it starts; fuel pressure regulator or the pump is weak.

yea i can try that. I am sending it to get tuned pretty soon, I feel like it isnt running no where near what it should be. Any thoughts on why gas would spit out the exhaust manifold when we crank to start it?