1968lsx

I have a 2001 6.0 engine out of a 2500 4x4 ,also have the wiring harness.i have searched and still found no answer.i have a 1993 4l80e trans that has been rebuild and has the updated wiring harness but no trans range sensor.
im putting this combo in a 1968 gmc .others have said they have deleted it out of the computer and others said they just left it unplugged.but the ecm needs to know what gear the transmissions in I think it idles up a bit in drive and in reverse. please help