I'm having trouble changing the passenger rear shock on my 99 2500

 

What kind of trouble? Please explain in more detail.

 

assuming corrosion is the issue - and its the top bolt, beat on the nut with a hammer to knock the scale off. Use a wire wheel next on exposed threads, then use a penetrating oil like PB-Blaster. It will come off. You can buy new nuts from the dealer if you want the tags that lock them from spinning.