1999 Chevy Suburban REAR NOISE

I have a 99 Chevy Suburban 350/4x4/5.7 and a few weeks ago I heard this clunking/clanking noise in the rear by the differential of my Suburban and then about a week later I noticed that when I stop my car it makes a subtle clank/clunk in the front. I know there are 2 U-Joints the (tail which is in front and rear end) Do I need to replace the tail u-joint also? . I took it to my mechanic and he test drove it, he said the U-Joints need to be replaced and it would cost $200. Now, I know the part costs about $25 the most. I usually work on my truck myself but I dont have a car lift to see exactly where the U-Joints are and I dont know what tools to use?? Can anyone help me and tell me where the u-joints are located so I can fix my baby myself since I dont like anyone touching my car?? Thank you.