Changing gear ratios in a 915 trans

[Charles Freeborn]

So, as I drive my 911 in more performance oriented situations I'm experiencing the downside of the mid 70's obsession with gas mileage. In a nutshell, I'd like to make 2nd a titch taller, 3rd too, 4th? and 5th a hair shorter?... in simpler terms take the spread from 2nd to 5th and even out the curve. I'm willing to sacrifice a few mpg at cruising altitude to do this.
I'm finding that my walloping 175 hp doesn't have enough pull in 3rd around turns, 2nd is wrung out too far, and I'd like to use 5th more on the straights.... Then I could use 2nd in the tight stuff, and with a taller 3rd avoid some of the short shifting into 4th on short straights.
How deep of a hole are we peering down here. Trans as is in good shape - maybe 15k on new sliders and synchros, all else checked out at the time. Total miles are around 120. In a perfect world this arrangement would perform well with a different (3.x) engine in the future. In this car I will NEVER put a monster engine, so cooling the trans and all that other hi-perf stuff is not going to happen. As cool as an LSD would be, that's not likely either.
Thanks!