Rb20 hesitation issue / lean issue

[DriftX]

90% of the time my rb20 swap will run really well, just a touch lean (wot 11.8/12.0 afr)

Every now and then while im crusing it will go super lean 19:1 ~ afr and stumble and break up real bad. Sometimes when I take off it does it as well and feels like it's "loading up" Sometimes I can drive all day and it doesnt act up.

I have verified fuel pressure under load by literally putting a fuel pressure gauge on the winshield. It is fine. Cleaned the tank, put a new sock on my walbro.

One thing I did notice is that car's vacuum is terrible. Sometimes it will idle super lean around 17:1 afr and hold -12 ish vacuum. However, when I disconnected the o2 and CTS wires the car idled like a kitten at 900 rpm and -19 vacuum.

Any ideas what could be going on?
I'm really stumped and have been working on this issue for months

[Yellow4g63]

lol my car gets 12" of vacuum but I have 270's. Maybe a lose coupler?