I'm unsure how this is happening I drive my truck regularly to work I only live 10 minutes away from work so my drive is not long enough to cause the problem but on the weekend'* when I choose to take longer drives with my family the clunking starts and feels very rough i hear my tires screaching in the back I feel like something is going to snap which I'm sure In the long run will make thing worse and more costly for me it is a c3 model which is awd drive (denali) any ideas or questions to help would be great

Any idiot lights on like "'disable AWD"? Scan for codes?

Are the tires screeching on turns or when brakes applied?

Last maintenance, like change of fluid in the rear end? Check fluid level?

Yes the tires do screech mostly on left haND turns I had a buddy walk beside the truck while I was turning he said he'* almost positive the was coming from the clunk was coming from the rear end and yes I recently changed the fluids in the t case and both front and rear diff I had a mechanic recommend I put a lucas solution in still didn't solve my problem I also noticed grease splatters up my drivers side wheel well I'm thinking the cv joint but it was done (not by a mechanic) by the previous owner I was also told by the mechanic my u joints need replacing and he said he could hear and feel movement in the t case with the truck jacked up I don't want to replace anything big incase it'* something small thanks for your reply as well I'm really hoping to narrow this down and fix the issue before winter I can see a loss of control coming my way if I don't as for the codes I tryed to hook up the reader and it wasn't getting a connection I've never seen that before bUT there is a check engine light on what gm doesn't tho my father in laws is on my step dad'* is on and my brother in laws is on