(ET) Drive belt slipping?

[tbamc <tbamc gbta net>]

Have started mowing this year and noticed that particularly in reverse 
but occasionally in higher forward gears, the mower pauses a couple of 
beats before moving.  Mostly level lawn, but does seem to be worse when 
trying to start on an incline.

I think I put a new drive belt on last year.  Is this likely to be the 
belt slipping? 

Thanks!

Thon
E12M