In heavy 320's and 321's - the last couple of thousand feet can be a challenge.
Because the aeroplane is very speed sensitive - i.e. it wants to get to or stay at the selected or managed speed quickly, you can get into a level, climb, level, climb scenario.
In this instance, selecting an achievable and conservative VS - 500fpm is a good start and selecting the mach HIGHER to keep climb thrust on, you will find that the climb is maintained, the speed may vary over an acceptable range and a smooth end to the climb is achieved. Getting to the last 2,000 foot point with extra energy (speed) is also a bonus and helps.
The big caveat is if you see a constant speed trend vector downwards, vary the VS to suit.
Other than that, I agree with others, managed climb and descent are usually the best unless you are late in which case its gear up, flaps up - 340kts until you reach your econ cruise mach, climb on that until IAS is the same as in the PERF page, then back to managed for climb and cruise. Repeat on descent and you will save about 8 - 10 minutes irrespective of leg length. Fuel will be unchanged for the sector length.
330 is different however, the D2 climb is pants - TWOFT
