In real life..planes cruise up to 35,000 ft + and cruise over 400 MPH easily. But, in FS2004 a B777 gets up to 27,000 ft. and makes about 375 MAX! Is there anyway u can make the planes faster?
Don't misinterpret indicated airspeed for true airspeed. At altitude, because of the less dense air, your indicated speed will be much lower than your true speed. At 35,000 feet, a jet will indicate approximately 290 knots but the true speed will be 460 knots. That's 530 MPH! Nautical miles are different than MPH. One nautical mile per hour or knot =1.15 MPH. Planes also have speed limitations at lower altitudes set by the aircraft manufacturer. The speeds in Flight Simulator are correct to real life. 🙂
Regarding altitude, a 777 or any other heavy for that matter should have no problems reaching an altitude of 39,000ft (this is a rather common cruise altitude in real life). I use FL 390 often and haven't had any problems with both default or third-party a/c.
This is not to say that you might not have picked up an a/c with a faulty .mdl file.