My 383 is weak!?

Thanks for the input so far guys. It has a 2.92 rear gear the deal is its got the small bolt pattern spindles and axles so I'll have to look for 84 and older trucks for parts which are very hard to come by here. Here's another question, will the axles from my pre-85 rear end work in a post 85 rear? If they will then this swap will be much more simple. What kind of RPM will I be running around 60mph with 3.55 gears? I am running around 2200rpm at 60mph with the 2.92s. I don't want to heat it up to where I can't afford to run around in it all weekend and pass anything but a gas station for sure. I'd like to be able to outrun late model 2wd bolt on Chevys and Furds. Around 9.0 in the 1/8th would be a good number to go for I suppose. What octane gas should I run with the setup I have? I usually run 91 octane but maybe I should be running 87?