Thanks for the passing on of the information...I appreciate the input...fortunately, the rest of the gauges I had working properly but I honestly and truly appreciate the fact that you took the time to try to help out. The GOOD news is that I put the truck up on the lift and decided to try CPWire and Chevy's suggestions

Yellow/Purple from transfer case pick up routes to engine bay which tied into my main harness...from there I simply tapped into that signal. My ECU is a 2000-2001 circa truck ECU so the pin out is on red brick, 20 and 21 pins. Chevy IS in fact right on the money as to which colors the wires are. I simply tapped the ECU into those wires. The ECU only monitors that signal for speed information, it doesn't appear to draw anything from it because the ECU now sees tailshaft speed AND the gauge still works. My seat of the pants impression is that the gauge is still reading correctly too...that being said, I will leave that final analysis for when I put the truck back on the dyno to double check.

So...thanks everyone for the input...hopefully this helps someone in future. My only concern is, according to my harness book, that 1999 ECU's don't have the same pin out and I am unable to determine the hi signal input to the ECU so if you have a 1999 ECU, this might not be the definitive answer...but it appears that post 99 ECU's should be good to go.