Here goes a lot of opinion....... The first thing I would say is you should not play with HP adjustments without a dyno. It is not a science......1_8 of a turn does not equal a certain HP increase. I would consider this as an option after ruling out some other things first, but only on a dyno. I agree, it seems really unlikely the clean grain system could use up enough HP to be able to notice. There are a couple tings I would sure look at first if I was wondering about HP. The first two things are easy to check. First (with the engine NOT running) push the throttle all the way to full thottle.......then go to the engine and check. The lever should be all the way against the stop and the over travel spring should be compressed. The next thing has to do with the drive belt. I have seen the snubber adjusted wrong so many times, by even mechanics, that it warrants a check. The adjustment nuts on the rubber snubber side should be tight up against the snubber, the nuts on the other side should be several inches away from the bracket.It is opften understood what they are there for. They should not be any where near the bracket. I have seen a combine traded because of low power. I spent less than a minute fixing the problem. With that many hours there are a couple things that for sure could matter with power. The valves need to be adjusted......correctly. Also the injectors need to be worked, the tips need to pass the gravity test. If you throw them up and they hit the ground the need to be replaced. OK, that was an attempt at humor. The tips need to be replaced regardless of what alot of people say. used injector tips are a waste of time. There are very few shops that do injectors right, including diesel injection stations. The bodies should be lapped and the tips replaced.Then the pressures set to spec......and even. Replace the fuel_water sep filter with the Cummins version for the larger combines, it will spin on the same base and does a lot better job. I have seen it increase injector componant life on these engines. That filter is an FS1000 fleetguard. Your gleaner parts man should have it......but dont remember the part number. Hope that helps. VSTK