Automatic transmission does not shift as properly as before after filter change

GM cars or any American cars with high miles better never change oil just add it or you can just flash it but keep filters and all gaskets same. If car less than 70k its OK. In your situation add to transmission Lucas but control the level of oil. Hopes its helps :)

I' ve been checking the transmission fluid level after a ride of about 10 - 15 miles on level ground. But engine has always been OFF ! Should engine be running during measurement ? Never heard about this. Small filter was included in the filter kit; I' m quite sure workshop did not miss it because I remember that I was discussing the tightening torques with them given in the installation guide.

Today I have re-checked transmission fluid level with engine RUNNING (gearshift selector in PARK position). This procedure is also recommended by my owner guide. This way I measured a fluid level below the min mark (1st hole in dipstick). With engine OFF level rises up to the upper mark / crosshatched area. Should I add some more fluid resp. Lucas 10009 or better not ? May the transmission be damaged if liquid level is too low ? I' m worried to overfill ! Any recommendations welcome.

from my own experiance in the past,i installed a shift kit,its called a correction kit it fixes factory faults,your trany will last 3 times longer run cooler,take off faster be better on gas! they run anywhere from 50.00 to 300 dollars.I wonce hit a bus pulled the motor & trany put it in another car and was off and running again with no harm to the trany! fords are known for bad trany shifting! never had a problem after shift kit install!