The TOTALLY accurate way to tell your true overall gearing...is below.

Park on a slight downhill grade with some downhill room....tires properly inflated, vehicle loaded as it would be when in use, etc.

Make a chalk-mark on tire sidewall facing straight down, and one on the pavement...have a helper roll the van one rolling diameter downhill, so mark on tire is again straight down....make new mark on pavement. Meanwhile, you get under van and count how many driveshaft revs equal one true rolling diameter revolution - that's your baseline axle ratio.

Now...measure distance between marks on pavement in inches, and divide that into 63,360 (the number of inches in a mile). This gives you TRUE axle revs per mile, and, axle RPM at 60 MPH. This number times baseline axle ratio (from above) gives you TRUE driveshaft RPM at 60 MPH....which is also engine RPM when in 3rd gear lockup.

4th gear RPM at 60 MPH is above number times OD ratio...usually .7 or thereabouts.

Hope this is useful...
Thank Matt