No reverse
 

My 1998 Chevy k2500 4x4 5.7L while in reverse I heard a pop and now I do not have reverse. All other gears work. Any ideas to what may have happened.?

Um.... transmission failure? Well, at least something relating to reverse. If it shifts to park and all other gears, I doubt it is the shift mechanism, but the transmission is electronically controlled, and internal to the valve body are electrically controlled solenoids that can fail, which are required to shift into different gears. Also gears, bands and other mechanical parts that can fail.

Is there a check engine light, or any codes set?