Reverse slow on ProSeries Craftsman

[Duncm1]

I have a Craftsman Pro Series 8200 Model 247.270421 approx 4-5 years old.
Yesterday I noticed when I mash the reverse pedal the mower is slower than normal. Forward is fine.
At times the reverse improved somewhat but then slowed again.
My manual says the transmission is sealed from factory. Could it be the drive belt? I've never replaced the belt.
A friend told me I'd have to replace the transmission.
I'm hoping he is wrong. Any ideas?

 

[Rivets]

I’m willing to bet on you and not your friend. I would start by replacing the drive belt, but also make sure that all pulleys are in good shape and the tensioner are is moving freely.