I am looking for help or any knowledge to this problem I am having. Any of the 2nd gen 3800 series 2 supercharged fwd cars(paired to the 4t65ehd).(sorry if this isn't in the right section thought this seems general enough)

Video:


What I've replaced:
VSS
fuel filter
Al606 plugs/duralast wire set
transmission fluid/ filter
transmission lines
all rubber vacuum lines
Cold air intake
injectors cleaned/ by running about 20 tanks with marvel
sea foamed and marvel upper engine cleaned.
been running M1 synthetic oil
2/3 coils replaced(one came bad )
MAF
front hub assembly(passenger side)
180 degree thermostat.

Description:
The Cat is on its way out, took it to one shop and we hit it and it rattles however no codes nor has it yet to affect flow. (accelerates fine) took it to another shop to get its back pressure tested, they told me its unlikely that the cat is causing my problems and didn't do the test. Followed up to a transmission shop, and they said the lack of consistency was unlikely to be a transmission problem. However its starting to be come more consistent. Now it does it whenever I have been driving the car for some time on certain roads. for example, can drive road A all day no problem, but when I drive road B every time it does it after about 30 mins or 15 miles, after I already am locked into overdrive with no problems. Some times it will do it at 35mph and have gotten it to surge and buck from 35-55. The Engine temp Stays normal The transmission shifts smoothly with dex III oil. I do get a rough idle every now and again. At first I didn't notice it but one day I heard its idle changing around and a popping noise and the car would vibrate in a consistent interval. I have never faced a problem as trying as this one and need some help. Any input would be appreciated.

 

Hey guys I want to thank everyone for looking. I got an update. I drained a quart of fluid, added some trans x, and then re-topped off my fluid. And I got good results, I am assuming I had some sticky valves and solenoids and the solvents in the trans-x cleaned it out much better then what I used when I did the first fluid change. I've been driving it pretty spiritedly over the past 2 days and I couldn't get it to surge again, and my shifts been pretty snappy and smooth too. I am going to go on a limb and say fixed. I will give an update in two weeks, to let you guys know if it is truly fixed.