1610 transmission problem

[MFP8055]

My 1610 has developed a transmission problem which first appeared after running about an hour. The machine has a new drive belt, and it does not appear to be slipping. The symptoms are weak forward drive when going up hill. It also appears to surge. If you back down on the hydrostatic level and then try to move forward it will make slow progress. When I first had it out with the new belt it ascended hills fine. Like I mentioned, it became weak after about an hour. Fluid level is good.

 

[diesel_nut]

When's the last time you changed out the tranny filter?

 

[MFP8055]

Tranny filter? I don't see any mention of a filter in the maintenance section of the owner's manual. My Bolens has a spin-on style, but nothing on the cub.