Automatic Gearbox playing up
 

Hi I hope you can help
I have a 2000 Xreg Chrysler Grand Voyager LE 3.3 V6 my gear box when cold works fine, but when gearbox is hot and you rev the engine past 3000 rpm the gear box looses all drive,and some times then slams back it to gear, slow the revs down and the gear all work fine upto 3000 rmp but not over. it has NO fault codes stored, the fluid is nice and red no nasty smells BUT it does look a bit thin. Has any body got any Idears???
Jason