I'm dubious of that trip computer anyway, especially if your motor is modified with 4 bar FPR etc. I see 45mpg average when going to work but if you actually work it out its more like 37 or there abouts, still pretty impressive i guess.
I also think that when modified and it comes on boost much earlier its easy to keep a steady mpg, although boot it a bit and kiss goodbye to economy !!
But as mentioned its a performance car, you want economy buy a soot chucker....
Oh by the way I put my motor into Revo "stock" mode the other day and it felt rediculously slow boosting to 7ish psi