Tranny for towing

[Stitch]

I have a C20 crewcab shortbed that I'm putting a 6.2 diesel in with a 700R4 for now...the 6.2 diesel is going to stay in the truck and probably get a turbo...We are getting around a 30 ft travel trailer and going to tow it with the C20...I know the 700R4 probably won't last long towing all this, so my question is...

What would be the best transmission and rear end gears to put behind a turbo 6.2 for towing and gas mileage?...I know that I'm not going to get great gas mileage towing the travel trailer, but I'd like to get decent gas mileage and I also don't want it to be a slug...I want to be able to go 70 in a 70 mph zone...it can be a standard or auto transmission...and I can change the gears in the rearend...it has 4.10s now...just need to know what would be the optimum setup for towing the travel trailer...I won't be towing anything heavier than that, and I'll only be towing that a max of probably 5-6 times a year...

thanks guys...