Need a little help ;)

Wifes 1990 Camry started to HESITATE. Monday it happened 1-2 times and
Tuesday about 8-10 times in 15-20 miles .
It's only when driving on the freeway at 65-70 MPH
No problems at all driving around town,or short freeway hops.
Passed Calif Smog OK, few months back.
Check engine light never came on. (it works)
Any Ideas ??

Which engine? What maintenance has been done recently and how long ago? Spark plugs been in there a while? How many miles on it? When it hesitates is it momentary or prolonged? Does it miss or feel like it's bangin on one less cylinder.

On what's given, I'd start with the fuel system and specifically the pump. At speed the pump is working hard to keep up. Put a higher demand on a weak pump and it can create hesitation. You could try changing the fuel filter first. Throw a can of fuel injector cleaner in the tank. I would shy away from timing since it's only at high speed. I would still have it checked to see if it's in spec. There is an outside chance the ignition coil is weak. Same scenerio as the pump. Only way to know for sure is to change it. Make sure your battery, distributor, spark plug connections are clean and tight.

1990 Camry,Auto,196,000 + Miles, Well maintain & running good. EXCEPT!

Thanks for the info, BUT ! I finally had a chance to test drive the wifes car yesterday and the problem is," it's shifting in & out of over drive,
quickly by its self." Randomly happens. Everything else seems fine.
What do U think ?/ Thanks again for your time

May be your engine coolant temperature sensor.

Replaced the Temp Sensor yesterday; Mama says," it seems to be OK. "
Keep U posted on this if it works. Thanks for the help Brian. Roofman