Do you happen to know how much of the 05 Tahoe harness was transferred to your truck?
I am assuming that you have a working electronic throttle body from the 05 Tahoe as well?
Full engine harness and under hood fuse box was transferred. Under dash harness and interior fuse box is from the 4.3/ 5 spd manual setup.
It can be done but you may have to run wires to the PCM from the multifunction switch. If it were in my shop I would check some cruise related data in the PCM . Next I would look for the mating wires in the back side of the large junction block. If they are there I would next check continuity from those wires to the fuse box and the PCM. If all checked okay I would then proceed with installation of the kit.