Something not right, but then you were running the Chevron one, rather than BG Products 44K.
If you feel up to a wee bit of experimentation, grab a bottle of 44K, and use that over two tankfuls as recommended.
It'd be interesting to see if the same pattern repeats itself again.

 

Most definitely! I was considering doing this with my redline oil change (I'm actually quite a bit excited to see the results, will probably send a sample to blackstone after 10k miles!).

But yeah, I went way above what the reccomended bottle was, the other one was too little, so I went for the too much hahaha.... Most definitely will try the BG Products 44K, report back and if results are MUCH better, i'll do it for the rest of the fam's cars.

 

do you guys roll with premium fuel or go with 87? i've heard that using the 93 will burn out somethin

 

i've used the 3M kit recently, definitely cleaned up the fuel system but i'm getting 20 mpg on avg with a 2nd gen gs300

 

93 will do nothing apart from burn cleaner and give a bit more range - I wouldn't listen to whomever fed you that line.
Your mpg is meaningless to compare as it has too many variables, but the 2GS is not as efficient as the 3rd Gen, and cars become increasingly inefficient as they age with mileage and wear & tear.

 

I have an 06 GS430 and I drive 50% highway and 50% city and get an average of 21 mpg, used Amsoil Pi that helped. Used BG44k in the IS350 and I get about 23.5mpg on average. Being summer the mpg is less too. Really want to see what it does in the winter.