Automatic transmission

I have an 89 ford tempo with 150,000 miles , my problem is when I put it into drive it slips for a few seconds, then goes into drive. once there it
shifts through all gears just fine without slipping. checked fluid it is fine, could this be major or just a fiter. P.S. does anyone know if this thing has any type of modulator or sensors that could be the problem. THANK YOU for any info that might help.
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