Sierra 1500/2500 1999-2002 /
Transfer case 246GM - Electric shift 27 Spline front input, rear slip output female spline front output.
Transfer case 246GM - Electric shift 32 Spline front input, rear slip output female spline front output
1999-2005
Transfer case 261GM - 27 spline front input, rear slip output, female spline front output (manual shift) LD 1500 only
Transfer case 261GM - 32 spline front input, rear slip output, female spline front output (manual shift) LD
These were the options on your sierra 1500. Good luck and hope this helps.