Sentry key won't work w/low gas

[jmags5]

99 GC Laredo has Sentry Key light come on while driving with approx. 1/4 tank. At 1/8 tank, it will sometimes start after SEVERAL tries & I've had to let it sit for 1-2 hours twice before it would start.
It has to be some kind of tie between the low fuel sensor & the Sentry system.
Anybody know which sensor that might be? I've recently had to change the one that won't let you shift out of 1st gear when the low fuel light comes on, so I would hope it's not that one. That was something like the engine speed sensor.
I work on the road so it's not always easy to just keep more than 1/8 tank in it at all times.