Need suggestions for transmission and rear end

[rally]

Hey everyone,

I understand there's a lot of factors to consider in this, and a lot of people ask the same question, but I wanted to start a new thread so I can ask my own questions as I learn. I'm not very knowledgeable in what my options are, but here's what I have and what I'm aiming for (and looking for help on):

I currently have a 350 engine, 350 transmission, and a 12 bolt rear end (not sure of any ratios).

I don't plan on drag racing the truck, but definitely want to be able to come off the line a lot quicker than what I do now (the response feels kind of slow). So more torque would be nice.

On the freeway, I'd like to get the RPMs down, but I don't have a tach, so I don't know what they are. Maybe they're in a good range, but they sound kind of high at 70-75 MPH (although, I'm running 18" front tires and 20" rear tires, so the speedo is off a bit. I'm probably going a little faster than that). Traffic in California is usually pretty fast, cruising around 80 or so, at least in the Southern half. I'm not looking to fly through traffic, but saving MPG while keeping up with traffic would be nice.

What I was thinking was swapping out the 350 tranny with a 700r4, hoping that would allow me to drop the RPMs on the freeway and save a little on the gas mileage. Maybe switching out the rear end to a different ratio would help, too, but I don't know where I'm at or where I should go with that.

What would you guys add/change for this setup to get a truck that's quicker off the line, but still decent on freeway gas mileage? Maybe the current configuration is good enough with a little tweaking here and there?