2007 16V Petrol model available performance mods?

[CloudDoesSPL]

Hi everyone, new here, glad to be here.

I bought an Auris 2007 1.4L 16V Petrol model about half a year ago, had to finish all the sound mods I had in mind, Speakers on doors, upgraded alternator, subs, etc, before posting here.

Had a question on what available performance mods are available for my model, both ECU-wise if possible, and actual mods I could do on the car, I went high up in the mountains a month ago and it struggled going up hills and such, had to use 2nd gear sometimes and 3rd on not so steep hills, mind you I had no AC on, no music playing loud, I was alone in the car, just cruising, is that normal for this model? Is it the 70-80kg of extra weight? I really don't think it's the weight doing this, no I hadn't done the same trip when the car was bone stock, should I be checking something? Is something faulty? I'd really appreciate an insight from someone who knows more about engines more than me, I know about the general electrical part of cars and anything electronic since I studied it.

Thanks for all the responses, I'll keep a close eye on the responses and answer any other questions people are asking.

This is my exact model: https://www.ultimatespecs.com/car-specs/Toyota/5184/Toyota-Auris-14-16v-VVT-i.html