so in your pre-flight planning you have not considered your DA and hadn't thought what your max speed in auto might be - you are pushing forward for range to avoid landing in the shark-infested custard and with the lever fully down, your Nr is decaying and your landing point is sliding gently up the windscreen..........:)

That's why we do 'auto revs' checks for the operating environment we are in.....

I worked with a supposed genius in a hot environment. He could not understand that the VNE chart for a 212 was based on DA. Then he bitched about the 87kt vne I calculated. I asked him if he actualy new what the TAS was at 6000 feet at 38C at 87 kts IAS...101kts. TAS. He looked like a deer in the headlights..he just didn't understand. He just hated seeing IAS less than 100 KTS... some macho thing ...Those VNE numbers may not be accurate ..long time ago..but I guess my message is that VNE IAS goes down with DA but your TAS does not go down that much.
212 man ...you are using common sense again ...stop that!
Sometimes we would operate in a -20...-40C environment in the winter and then change to +30c for the summer. Checking outo rpm was a normal spring/fall check event amongst other checks. Especially if we changed from operating from bases at 1000ASL to a mountain environment where you were starting from 5000ASL.

I try hard to shake it off, but it seems to stick......

Rather missing the point - of course the aircraft should be correctly rigged for the conditions but you don't do your autorev checks at Vne for auto do you?