TDTM

You let off the throttle is what I mean by coast in drive still. And I did center the u-joints. The vibration feels like it is directly under your feet. And it modulates at 100 kmph or higher I did also change the output seal on the transfer case to the rear shaft because it was leaking and topped up the transfer case about 700ml of fluid I used the transfer case fluid from gm as well. And the vibration was under the drivers side floor panel before all of those changes. And still there now

So I am wondering how I tell which transmission I have on my 1999 gmc Yukon Denali. I have a bad vibration on coast I have changed both u-joints in the rear shaft already and it happens in 2wd. My 4wd is electronic shift. Any ideas on issues and which transmission I’d have or a way to find out? I’ve posted my RPO codes as well