I replaced my 285s with a set of 35" and was wondering about new gears. According to the charts I should run 4:10s to replace the 3:73s. Also, I was thinking about putting a limited slip or manual locker and was wondering if anyone has some ideas for this. I have a 1999 Silverado "classic" with the Autotrac, but I'm not sure what size axles the truck has. I do a lot of hiway driving and mud/trail riding on the weekends.  

If your looking at a chart it's way off there...unless it is specificly for the 4l60 auto that has a .7 OD ratio..or do you have a manual?...thats .73...
most charts are figured using a 1-1 ratio, that your tranny being held in manual 3rd gear...It is nearly 1000 rpm away from being correct!  

a 4.88 gear will be the best bet there...a 4.56 is the closest match to the stock ratio. it'll turn about 2130rpm @65 mph with the 4.88 and 35" tires....NOT 3050 as the chart sugests!

the stock set up with 3.73 figures out to be about 1850 @65mph. the extra couple hundred rpm's help overcome the rolling resistance of the  larger/wider tires.  

What "chart" are you using??? The one that tells you how to make OD next to useless?  I agree with Mudd, you want bare MINIMUM of a 4.56 here with a 4.88 being a better match.  

I have an auto trans. I was looking at the chart on the 4 wheel parts website and putting in my old tire and gear size. Will the 4.88s be good for highway driving as well?? What about a locker, I was thinking of getting a pair of detroit true tracs or auburn limited slip. Does anyone have any experience with them?? Thanks for the help.  

the 4.88 is great for a daily driver.....just over 2100 rpm's with the 35's @65mph....which is a couple hundred over the stock gearing and tires.

the chart gives you numbers for operating in 3rd gear only not 4th.

both lockers are good ones, its not a good idea to run them in the front due to weak axels.