[New feature ideas]

Just a few thoughts for future features.

1) Add a layer preview stepping function where you can jump 1, 5, and 10 layers at a time.  The scroll bar is very useful most of the time, but not very accurate when you have over 1000 layers and are trying to troubleshoot a print.  Typing in the layer number each time gets tedious in very short order. :(

2)  When at less than 75% fan speed on my reprap the layer cooling fan will not start.  After I slice I need to go in and replace M106 S  with M106 B1 S to bump the fan to full speed for 1 second so that it will run at lower speeds.  I think that this would be a boon for people who do not have an Ulti, but still love Cura.

3) This comes from the engineer in me...   I think that if the outer layer was offset by 1/2 layer height it would increase the strength of printed parts, help with delamination and give a smoother exterior.  The down side might be in the loss of details.

Any who...just my 2 cents worth

[Different speed at different high]

It sounds to me like you are over powering your hot end. Try bumping the temp 5c or so. When the print is slowed down the hot end has more time to melt the incoming filament, but at higher speeds it cannot. You might also try Post Processing ->Modify G-code ->TweekAtZ>