Why is it so peppy when HV is low? & Spark plugs?

So I got my 2010 Prius at 163k in 2017 and it's now 2020 with 183k. According to Toyota logs it had its plugs changed at the 120k service interval. It has burned oil since I've bought it. I wonder if I should do plugs, because I'm taking all that off soon, to do a lift kit. I do not understand Toyota's maintenance interval system. Any other brand, even motorcycles seems clear as day. So I don't actually know when it was supposed to be done next.

The best I've ever gotten with it was 41mpg calculated at the end of the tank. For quite a while I've been averaging about 37mpg. Acceleration with this car has always been hit or miss, even limped a few times. I also have "vtech" at around 55mph. Which last time I brought that up people thought I was crazy. I have noticed that either when the battery is 2 bars and the ICE is on while in a parking lot, or going 70mph down the highway, is the only time it seems to have any pep and the throttle actually feels attached.

Going into detail/rant on the above paragraph.
I seem to be at the will of the hybrid system, sometimes it will actually use the ICE and accelerate away, or other times it will just kind of grunt the ICE at a low RPM and accelerate pretty slowly. Couple times I've pulled out into traffic and I can get up to 20-30mph decently, but then it starts to grunt the ICE and accelerate about 1mph ever 2-3 seconds. Luckily that's only happened 2~ times. I think the summer heat is a contributor.

One time I had to pull over for a ambulance or something and when I went to pull back onto the road, the traffic behind me was already back on the road and catching up. The prius was "downshifting" or "winding up the rubber band" and accelerating so pathetically slow that I pretty much cut the person off... Which I find if I think I'm going to cut someone off, it's going to be a super bad cut off because of how long it takes the prius to actually "downshift" and then start accelerating. It usually takes tons of planning and gap to properly overtake someone. Sometimes I'm barely touching the gas and I'm like ok car, calm down, why are we going so fast? (I only drive in normal and EV) I don't understand why it seems like the hybrid system has vastly different performance output, despite flooring it.

I've just been living with it, operating the way it does. I've also noticed in EV the eco bar will move but my position on the gas pedal will not. I'm not sure if it does it in normal.


This paragraph is probably useless but I don't feel like I should delete it after typing it up.
I do like MPG but am kind of caring less, but more is always good. I recently put some oversized AT tires on it, 215/70R15 H Geolander 015's (not LT) For my first few work commutes, I actually got the same MPG, if maybe -1mpg, but my speedo is now off 3mph (60 reading is 63 gps) Then one day I filled up and then I've been getting about 31mpg on my trips when I used to get about 38mpg. (Used to read I think 3mpg high) They grip so much better and are more comfortable. (rain and idiots)

Thanks,
Higgins909

 

I bought it in Feb of 2017 with 163k~ and now Dec 2020 it has 183k~. I do not drive much. I did about 5,200 just in commuting to work. I moved in Dec 2019 and now I'm doing about 3,822 miles a year just for commuting. It's behaved the way it has, since I've bought it. I was thinking plugs needed to be changed every 120k and then I heard something like changing them when you hit 150k. Under good conditions. If it's burning oil, maybe they need to be changed more often?