4.10 gears

Hi! I have a 6.2 Diesel Silverado that, according to a website I found,
has rear axle ratio of 4.10, which I had assumed all along. It has a
700R4, and seems to 100rpm/3mph-- IOW, 1500= 45mph, 2000=60. I was
wanting to change the rear end to somewhere in the 3.50 range, but then
saw a website on transmissions that gave the OD ratio of a 700 as about
68. I am afraid that 3.50 +/- would be lugging the engine in OD. FWIW,
truck is a 3/4 ton extended cab and has a liftgate on it.I do not plan
to tow anything heavy-- maybe a car on the tow dolly, or a trailer with
about 1000 lb on it. I can't see going to the expense of changing the
rear end to just the next higher ratio from 4.10.  Any comments and
advice will be greatly appreciated.  Thanks  Larry