The first thing you have to understand is what exactly all the manual lever positions do, then maybe you'll understand it better. 1st means only first gear, 2nd is usually 2nd on honda's and only second so you can actually take off out of 2nd gear if you have it in manual 2nd i believe that's if your in the snow so you don't spin the tires as easily. Now if you start off in manual 1st upshift to manual 2nd it will shift to 2nd onces the govonor pressure inside the tranny surpasses the throttle pressure. Now d3 is third, but it will downshift and upshift just like d4, with overdrive lockout so in other words it won't shift into overdrive. So if you don't want it shifting to overdrive drive in d3 and you will still start off in 1st from a stop and automatically shift through the gears like normal. There is no beneifiet or down effects of manually shifting your tranny. If your doing it for acceleration it's pointless, because your tranny is designed to hold shifts under maximum throttle pressure to about redline. If your going 80 and want to slow down faster manually downshifting is fine provided your not going to fast for a certain gear i.e. I wouldn't reccomend downshifting to 2nd until you get below 50. Downshifting provides engine braking. Other manufactures have more clutches applied when you downshift to take stress off parts if you deside to manualy downshift, but honda trannys are a completly different design and use clutchpacks to hold a gear directly it's basically a manual tranny with clutches. Also to clear something else up your torque converter is basically standing still at higher rpms because it's reached stall speed so it's not making much heat there because it's not slipping anymore however at higher rpms your torque converter is still spinning your pump at the same speed as your engine becase that part of the touque converter is always spinning with the engine but all excess pressure is bled off from pressure regulator valve so your not just building up pressure otherwise you'd ballon your converter and take out your crankshaft. Hopefully that clears things up.