Mazda E2200 Summer Issues

Good afternoon all :-)

So, l have a mazda E2200 glass van YOM 1990, 180K on the clock, just been serviced. Oil and water up to scratch. Normally starts with half a turn on the safe starter. Very economical at about 9 cents/KM whilst driving in the inner city traffic (including some challenging hills)

My main concern comes as the following

Since summer has started (here in Malta it can go all the way up to 35 degrees), it has lost some of it's peppiness shall we say, it became a bit sluggish. Not very sluggish mind you, just if usually going up a hill it needed 1/4th of a pedal at 3rd gear, now it needs half a pedal at 3rd gear.

Everyone including mechanics said that it's normal for vehicles to experience that due to the heat.

Does that make sense?

Or am l missing something?

Heat most definitely affects performance. You'll notice on cool evenings that it will feel like it has more power due to the cooler, denser air.