You need to wire the VSS on the tailshaft housing of the trans to the PCM. The Green/Black wire of the VSS should to pin 20 on the C-2 (red)connector of the PCM. The Purple/white wire should go to pin 21 of the C-2 connector. Pin number 50,(dark Green/white) of C-2 should go to your speedometer.
According to LT1swap.com, you must add a pin/wire at pin#38 on  the C-2 connector. This is used to run '96-'99 truck fuel gauges. I would imagine that this output signal must go to the location where the old PCM supplied the output signal for the guage to work.
				
			 
			
		 
			
                        	
		         
			
			'93 Chevy 1500 4X4 ECLB with a '99 Silverado LQ4 6.0 and '99 Escalade 4L60E.     SOLD IT!!
New toy: 2001 2500 HD 4X4 Extended Cab Long Bed
John