well, since the transmission initialization did not work, my next thought was that maybe you only had it in 3rd gear in the ESP position and it was wound out....but other than that this has gone beyond my knowledge, you should talk to your dealer, you should still have warranty....maybe

 

My '07 Rancher 420 ES will do 56 mph, but it will only hit it just long enough to say it was there and kicks down to 55 mph.

You might not be shifting into your 5th gear. A 35 mph top speed sounds like 4th tacked out. Is it still under warranty?

 

Taking to shop.

 

Shop tells me they find no problem. 37 to 39 mph top speed. Anyone have any ideas on oil? would a synthetic oil make a difference?