autopage 720lcd and rs 860lcd

I have a 1999 Tahoe and a 720LCD remote start alarm and love it!  I was wondering if I purchased the RS-860LCD if all the same wires and harnesses will work.  The fact of rewiring everything doesn't sound like fun to me! I like the newer FM/FM remotes and additional channels that I might can use on the 860.  If anyone has done this, let me know.

PS. Also, I have downloaded both manuals and it looks like all I would have to do is switch the main box.

Greetings Everyone!

I am a proud owner of a 1999 Chevy Tahoe with a Autopage RS-720LCD remote start/alarm.  I have had the alarm installed for 4 years and then I saw the new RS-860LCD.  So I purchased the new unit and installed it.  I know my trunk does have a Passlock system and I will be cutting the old harness wires and just wiring up the new harness for the alarm.  I have done so, and now the alarm is programmed and works, but the truck will not start when I try to start it with the key.  I have not learned the tachometer just yet bcause I was not planning to remote start till the winter time.  For now, I just need the truck to start normally with the key in the ignition.  Could it be the starter disable kicking in or the Passlock system keeping it from starting?  I think it is the Passlock system because I know the started disable only disables the starter when the alarm is in armed mode.  I have never wired a alrm from scratch and the alarm was installed by a reputable shop in 2002.  Please advise on what I need to do next to get this truck to start like normal with the key in the ignition

1999 Chevy Tahoe

AutoPage RS860-LCD

Does your vehicle try to crank??  Are you using a bypass for it?? which one?

The vehicle does not try to crank with the key.  However, I can remote start the vehicle with no problem and be on my way. 

I don't know if the previous installer used a bypass kit or not. If so, where would the typical installer hid the bypass kit?

Thanks for all your help.