i have a 2000 kubota b21 with 1200 hrs.. last week i was brush hogging a account i do 3 times a year.. the tractor has a tough time due to the fact one part is a very steep hill that must be brush hogged going up and down due to the grade.. i usually have to leave the hood up to keep the tractor running cool... well last week the tractor was not really running hot i have ran it up to three quarters without this issue.. temp was about half way up compared to normal running temp a quarter up on the gauge.. the the tractor would start to idle all the way down then after 15 seconds the rpms would pick back up.. thus making the hydros very doggy.. i had to finish the hill with a ztr this is how bad it got.. i keep up on oil changes and hydro filters air filters fuel every year.. any suggestions on what to check would be greatly appreciated thanks chris