Erractic stumble/hesitation off of idle 126 coupe

I have a 380 sec w/162K and for the past 3+ monthes I have an erractic hesitation coming off of idle. It isn't all the time. Nor does it occur when cold, hot, warm, just when it feels like it. This can prove to be annoying especial pulling out in traffic, when I give it gas and it hesitates then it "lites" off. I have recently replaced the timing chain, O2 sensor, exhaust system from pre cat back. Fairly recent plugs, wires cap rotor fuel filter.
It also seems that when the hesitaation is gone the car seems peppier, could be my imagination.
Any suggestions as to what to look for, tests that I can run, I am fairly mech. and have access to a lift and repair shop.
Thanx
S

[Benzmac]

A set of fuel gauges may tell you a story. I would connect fuel pressure gauges as outlined in the manual and drive the car.