Heated o2 Sensor Diagnostic Monitor

[94 Jimmy]

2000 Yukon, 6.0L, JBA Headers and exhaust, 70,000 Mi.
I had to clear a P1870 code from the ECM, this has the unfortunate side effect of clearing all of the Diagnostic Monitors. I've been through the suggested GM Drive Cycle several times but can't get the Heated O2 Sensor and Catalyst monitors to flip to complete. My OBDII reader shows a normal upstream O2 sensor graph and the downstream O2 sensor shows a nice lean exhaust. I replaced the upstream sensors just in case, but no luck.
What is the computer looking for to complete the Heated O2 Sensor monitor. There is no circuitry in the heater to monitor current or voltage to the heaters, just a direct connection to the fuse. Does the computer look at the time for the sensors to go to closed loop, if so what is the time. If I leave the key on the sensors get warm, so the heaters are working, but is the steel tube exhaust conducting the heat away faster than the stock cast iron headers and slowing the time to closed loop? Could I heat the area around the sensors with a torch before I do a cold start and hurry the transition time?
I need to get these completed so I can SMOG this thing and get to work on the transmission.
Any ideas? Thanks.