The PRU rise and fall times are 1.00 - 3.00 nSec. Your scope probe or application circuit may be limiting the slew rate. Another possibility is your oscilloscope input is bandwidth limited. If you are using a 1X scope probe it will contribute significant capacitive loading and slow the edges way down.
Keep us informed with your progress and good luck.
Cheers,
Lowell Bohn
Chief Engineer
Basis Vector LLC
(303) 249-3763