Airwire and USA Engines

I have an Airwire system in a trailing boxcar with a power lead to the rear of a USA F3A. I also use the same configuration with the USA GP7. I don't double head them, only running them solo. At most, I get only one hour of running time. I took one of the motors out of the F3A figuring the run time would increase. Nothing doing. I haven't checked out whether the batteries are in proper working order. When I run, I always charge them fully. Beside a possible battery problem, are there any other things I should be looking for. Has anyone else had this problem ? I know USA engines are power hogs, but ???

Thanks in advance.

Pat McCarty