Ford Falcon: Transmission problems

Immediately on collecting my 2005 BA Falcon ute after the automatic transmission was rebuilt in 2012 I was concerned that it was not changing correctly. It got worse, and a month later it was slipping when I put light pressure on the accelerator and changing into top gear between 2500 and 3000 rpm instead of 2000 rpm. The auto transmission repairer couldn't find any problems when they drove it. A couple of weeks later there were more problems, changing up and down from top gear, slipping out of gear and not holding, and it was not kicking down when I went to accelerate. The transmission was replaced in Dec and was 80 percent okay when I picked it up this time, but after a couple of days it was slipping when I accelerated and changing at 2500-3000 rpm and the fuel consumption has increased. Now the repair shop says it's either electrical or a sensor problem. Where I can get help to sort out these problems, as I feel the repair shop is unable to solve the issue?