On occasion after backing up when I put the transmission in drive and it seems it slips out of gear and the engine races. This lasts for maybe a couple of seconds then goes into gear.
any suggestions of what it might be?

 

Dirty/plugged transmission filter ???

 

I doubt it. I had the transmission flushed at about 60,000.

 

And 60000 is 10 miles ago? 1000000 miles ago? I would make sure you have enough oil in there to start.

 

I have about 73,000 miles now.