Whats everyone running for gears?

4.10 SG w/28" tire. Bought a new 70 duster 340 w/ 3.91 SG, 833, and E70 14's (24.5 dia?). Drove it 15 years and 200,00 miles with only a valve job.Had two trips from MN to CO and about 50 runs down the strip (6000 sp). Reduced engine life???