Not sure about '90, but in '88 it was the same as my car - 3.27:1 for both manual and automatic transmissions. You can verify with the tach reading at 65 MPH:

(65/60)837(3.27)(0.8) = 2372 (manual)
2372/0.8 = 2965 (auto)

837 is the revs/mile spec for the OE 195/65R-15 tires, 0.8 is the top gear ratio for a five-speed.
If you you use another check speed, say 70, then replace the first term with 70/60, At 60 this term becomes one, so it can be ignored. If an automatic just drop the last term (0.8)because top gear is 1:1. The speedo/tach relationship will not change if different revs/mi tires are installed, but the speedo will be off the percent difference in revs/mi from OE calibration.

You can also rearrange the above relationship and compute the axle ratio with an accurately observed top gear tach reading at any speed. With an auto make sure the reading is on level ground to minimize converter slippage.

Five speed ratios are 3.86, 2.18, 1.38, 1.00, and 0.80:1.

Duke