350 performance and timing issue

Okay, I've got a multitude of questions and I hope there is someone out there that can assist! I have a 1989 5.7 350 TBI motor that has Edelbrock performer aluminum heads, a crane Powermax cam and a VENOM 400 engine controller. I was looking into purchasing a Edelbrock fuel injection (conversion) intake and getting rid of the VENOM. It hasn't proved to have a "outstanding effect" performance wise. Has anyone switched over from TBI to MPFI and noted a vast difference in performance and any change in fuel economy?
Secondly, it seems I can never get the timing just where it needs to be. The engine stumbles (hesitant) going up hill or lightly loaded and when idling. I know there is a timing advance connector, but I only find one side of the wire coming out of the wiring harness (could be an O2 sensor wire, but there is also one on the other side for that), not the other side from the distributor(?).
Is the GM HEI automatically advanced? If so, how would you time it in relation to the advanced idle if it can't be disengaged? Please advise! Thanks
Steve  

My advice TPI from an early 90's camaro, Upgrade the injectors from the camaro to those from a vette and take all computer and wiring and sensors with it.