Getting Frustrated , A Rant, I Guess!!!

[Already Gone]

My truck has a 396 with a TH400 and 3:73's ... I'd like to get better fuel economy on the highway and know I either have to go to 3:08 gears or change to a 700R to do that. My research tells me the ideal scenario would be a 700R with a 3:42 posi out back but that would be way expensive.. If I could put the 700r in myself I would do it in a heartbeat but it would cost me 8 to 900 to have it installed properly by a local reputable shop and I'm not counting the cost of the 700R. After doing some price checking a new 3:08
(12 bolt) with posi would also be 7-800 to purchase and then again I cant install so I'm guessing I'd be looking at another 500.00 to get it installed properly. I guess fuel economy costs !!!!
I get 12 mpg on the highway now and I'm thinking in ideal conditions doing anyone of theses changes I'd get 16/17MPG on the highway.. I probably drive 3 to 4000 miles a year and doing the math I'd save ( on our Canadian gas prices) about 400.00 a year.. I dont know if its worth the money to change anything..

I'd like to hear board members opinions on this..