Keep same tempo.
I've been learning a quite difficult piece and I'm noticing through playback that I have a tendancy to either speed up to slow down on some bars where it should be the same speed through unless marked otherwise e.g. Poco rall. Granted I slow down moreso when I reach difficult phrases but rush parts that I know well.
I haven't really practiced much with a metronome but as I play with headphones in I'm not sure how I could hear it 😃
Also I want to ask for some feedback in regards to my current piece - Go The Distance (from Hercules), it's a step-up in difficulty and I know that it's not advised to play pieces that are too difficult, however the past week I've started, my progress has been steady enough and I've been really enjoying learning each parts, and coming across techniques that I've not done before, especially in regard's to my left hand, which isn't used to moving so much 😂
Here's a link to a similar arragement (I've reached to around 1:45 ish on the arragement I have) by Master Keyz:
https://www.youtube.com/watch?v=ovzX6yNfJpQ