Fixed my flaky tach issue. It turns out the output pulse signal in the vortec pcm was set wrong and was causing the stock indash tach to jump around. I reset the signal back to the stock LS1 4 count per rev and then using my dakota digital converter I was able to stabilize the gauge. Now it's smooth and responds correctly.
I also figured out how to activate the 'tow/haul' mode.
Normally the silverado trucks use the body control module to respond to the truck tow haul button and sends a request over the serial data to activate the secondary shift pattern. By activating the pin 71 in the blue connector, it now responds to a simple ground circuit request and momentary push button switch. By pushing the button once, the circuit from the pin 71 is ground to chassis and the PCM commands tow haul mode and raises the shift points, holds the gears longer, and firms up the shifts. Push the button again and it reverts to normal mode.
pretty cool! I can go back and edit the shift patterns later as needed.
1994 FZJ80. Elocked, MAF 3/2 Lift, BFG 315 KM2s, stock 4.10s, ARB bullbar and a Warn 8074 winch.
powered by an all-aluminum 335hp L33 Vortec V8
2004 Kona Stinky dee-lux.