Lower rpms

[biggpoppa3]

I've got a 84 1/2 ton c10, 2wd swb with a mild 350, th350 trans, rear tires are 265/50/15's measuring 26 inches around with a 10 bolt rear end with 2.73 gears. My problem is I do a lot of highway driving and the truck revs really high at 70 its around 3000 rpm. I have been wanting to put in a 700r4 but money is tight right now, and cant have the truck down for long. is there a different rear end I could put in it. or maybe a different size back tire I could run and if so I need to know what would be the same width tire that I have now as my rims are 12 inches wide any help would be great, thanks