Give us a little more info - slow reverse......I take it that it is slower than you think it should be? OR something happened and now it is slow? At 2.8 mph in low range.....that is slow ! but normal!
Is is slow in H range? Does it speed up or slow down in different RPM ranges?
Is there something in the way of the pedal in the reverse position? Stick or something? Have you checked fluid level? It is still under warranty - have you contacted dealer?