If it were me, I would be changing the cam, intake, rear gear, carb, and converter

My combo would have been a solid roller 280ish @ .050 .700ish lift, single plane with a 1050 dom, 5.13 gear and around 5500 stall and let her eat .

With that being said, the things that in my mind absolutely need to be changed are the cam and intake. There are lots of great solid shelf cams that are way better then the .620. The intake is really hurting your combo as well and I believe it should be changed. You're geared perfectly for and have the right converter for a big block stroker, unfortunately you have a smallblock!!

As Mr. P stated, you need to rpm the motor to reach it's true potential. Shifting it at 6000 isn't doing that.