Cruising speed

If you set M .84 at FL 120 of course you're gonna get overspeed. You gotta be at the prescribed cruising altitude. What is it for the 777 - something between FL 340-370?

Anywhere above FL280 and you shouldn't get an overspeed warning. Try somewhere between .78 and .82. What is your IAS in the overspeed? Look above / below the speed tape, does the mach figure reflect what you've selected on the MCP?

Real life pilots are flying real life aircraft in real life conditions... You can't seriously expect the same from a sixty nine dollar simulator. Thus the variances from Real Life.

I have the same problem getting the full motion feel of flying to work in FSX it just doesn't feel the same as when I'm out in the real world 737 simulator, of course it costs about sixty nine million. 😉

Well, when i move the MACH setting, the knots setting jumps a lot. example:im at 380kts=M0.66. i move it to M0.84 and the setting becomes 990 kts!!

You can't jump from M.66 to M.84. (I still don't know the cruising altitude for your 777 - you could help out a bit here)

BEFORE you switch to Mach, climb to FL220. Let the aircraft settle at about KIAS350. Once it's settled, keep an eye on your KIAS and now flick the switch to Mach. If it automatically changes to M.66, wait a few moments and let it settle again. Begin a steady climb to cruising altitude and as your altitude increases, you can gradually increase your Mach setting until you've reached cruising altitude.