I have a similar problem on a 99 SVT with about 19000 miles. It never gives me problems when the car is cold started. Typically it shows up when the car is driven 10-15 miles and parked for shopping. Upon start up it is very difficult to shift into reverse and forward gears SOME of the time. Other times, it shifts fine.
I have found out that when it is difficult to shift into reverse, it will shift right in when the engine is shut off. This car is still under warranty and I will take it in and post what they find. You can check the dialog of the other topic I started on a shifting issue by searching on member #6833.
Good Luck
