6-speed???did you ever figure out the issue? my Genisys OTC cant connect . i do get a MIL but only on the highway and when i shut down and restart it only comes back on during highway use (91 k1500 5.7 6 speed) .
When my '88 K1500 5.7L TH700 set a code at highway speed only, it was a failed O2 sensor sending false-lean info to the computer.
I don't know the Genysis system. Can't help with that.