2007 GMC Yukon PLEASE HELP! Any info would be great

[Morfias4Twenty]

Ok So I was driving at like 5 mph In a parking lot, when the wheels lock up hard, screeches on the pavement and the trucks starts rolling again, I stop to see if maybe I ran over something, I see nothing then Put it in drive and the trans won't engage, So immediately think " damn my transmission just went out". But I drop the shifter all the way down To 1 and it drives, then I shift it up to 2 and its still driving.. At a dead stop the transmission will engage On 1 and on 2, It will not engage on 3 or on D. BUT I can shift the transmission manually From 1 to 2 to 3 to drive and it will drive with no issue.. I also have to down shift it manually because if I don't once I'm at like 20 mph it won't catch. It will just rev like I'm in neutral. It also makes a vibrating screeching sound some times.. This just happened 2 days ago..
Am I making any sense? Does any one know what might be wrong? Has any one experienced this before?
again its a 2007 GMC Yukon with 79k on it

The Trans never slipped it always shifted nice and smooth, any info would be great..
don't really know if the trans is a 60 or an 80.. How can I find out?

Thank you all in advance
Roger