Im having problems finding out what diff I have... the tag says 2.70 .. im tierd of running 65 mph at 3000 rpm how and wich is the better gear ratio or and number I need to streach it out? thanks Mike

 

65mph @ 3000rpms most likely isnt the 2.70 stock gearing. Sounds like 3.55s or possibly3.80s.

 

You have 3.55 gears. You can swap in a AOD. The overdrive will do wonders for your gas mileage and still give you the launch off the line. Or you can just put in some higher gears...(numerically lower)

 

3000 rpm's around 65-70 would be correct if your running a std trans or a automatic trans that would not be a overdrive trannie
if you have a 9 in a 247 is the highest i think they made factory and that would only slow your engine about 250 rpm's, the only thing to do if you want to cruz on the highway it to install a overdrive trans,
that ratio is the reason lots of the older cars were wore out when they hit the 75 k mark, the engines had just revved there selves to death ! overdrives add lots of miles to the engines over the long run