Prusa I3 Z Axis Issues

Hi guys, hopefully someone can help shed some light on some issues I'm having.

I have built a Prusa I3, and all things considered, works fairly well, I have had a few minor issues along the way that I have managed to sort out, except for this one issue I'm having now which has me baffled. I'm using Pronterface, and using Slic3r to slice my objects.
The issue I'm having at this stage is with the Z Axis. When I print something, the printed object is the incorrect height (too short). For example, if I print something that is supposed to be about 100mm high, it will end up being about 80mm high. Printed objects tend to be about 80% of the height they should be, I printed something that should be 50mm high, and it ended up being 40mm high, etc.

In troubleshooting, I homed the Z axis, so the nozzle was almost touching the bed, like 0.3mm or so. I then moved the Z axis up 100mm through pronterface, and measured from the nozzle to the bed, and I got pretty much spot on to 100mm. So the z axis is moving accurately through manual commands.
I made a very basic model to calibrate and to take measurements of a printed object, it was 100mm on all axis. After printing and taking measurements, x and y were spot on 100mm but z was around 80mm (cant remember the exact measurement but close enough to 80mm).
I then made another object that was 50mm on x y and z, and printed that. The finished object was 40mm on the z axis, but I noticed that at the end of the print during the last layer that the LCD display on the printer was saying that the z axis was at 50mm....
So how can this be? how come if I move the z axis manually if will move the correct distance, but when it prints an object it doesn't? It has really confused me. I'm fairly new to 3D printing and still have a lot to learn, and I'm pretty happy with how this has turned out considering I built it from scratch, but this is the only thing that is stopping me from printing some decent objects that I can use.

Hoping someone has come across this before or may have an idea on what I can do or check to fix this issue?

Thanks in advance guys!

decrease your max feed rate for Z in your firmware

eg in marlin


#define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25 }

the 5 is the Z feed rate and this is to fast for a M5 based z axis

change it to a 3

Awesome, thank you! I'll give that a shot tomorrow.

Thanks for the reply!

Thanks man, you're a superstar!

I had a look at the settings in the firmware, I found the Z feed rate was already set to 3.3. I changed it to 2, just completed another print and the height is exactly as it should be, so problem solved!
I can't imagine there would be any issues with leaving it at 2? I've done a bit of reading on the max Z feed rate and 2 seems to be a fairly accepted value from what I have found.
Anyway, thanks again! very much appreciated.