Oxfordcar3, I think I have the same machine. Mine is slow and labors the engine when cold. If your problem is when warm I don't know, but hope you will post here when you figure it out so that we will all benefit. What oil did you use?
Does it warm as well just not as bad I used the recommended engine oil don't remember weight off hand however it was run for unknown amount of time with hydraulic fluid in it will post if I figure it out
Probily needs new seal kits inside cylinder mine did the same thing although mine is a t3-15 and much older I also have a 14hp kohler single cylinder where you probily have a twin. Another thing you might look at as well is the govenor make sure its set right. I set mine back to factory spec's and only run my terrmater at 1800 rpms and when it bogs down it kicks it up to 3000
Sam