engine shutter w/ trans slip?

i have a 95 thunderbird v8 that has an engine shutter around 30 mph and at 60 mph. its not as bad when the car is in over drive. recently we put synthetic trans fluid and the shutter was not fixed. but now when you start the car and put it into drive it takes about 3 seconds to get in gear and when i sit at a light or something, ill have the same problem when i go to accelerate, even though it was in drive. that will last for the first 5- 10 min. of driving after the car has been parked for several hours. any ideas?

I had a similar problem from 55k to 65k miles. then i had enough of the issue. i had the tranny flushed for ~$65. it ran smooth after that. Currently, i have 89k miles on my bird.

You should probably get your's flush right away because you shouldn't mix fluids; it can cause you more grief.

jnn is right, you shouldn't mix fluids without first draining pan of old fluids first. Also, synthetic ATF is not recomended for the 4r70w trans these cars come with. The viscous properties are not the same, sticking to Mercon-V is your best bet. Trans filter could also be something to look into.

The shudder you are refering to is from the overdrive in the automatic trans. What aparently happens is the clutches get burn or rub spost in the surface and that is where the shudder or slip comes from. They are correct ...never intermix trans fluids newer fluids are not designed for this perticular transmission. I had a transmission fluid complete evacuation done at local trans shop $65.00 that drains also the converter. Once refilled with corect fluid the shuddering stoped. I also added a small red tube of Dr. Trans Instant Shudder Fix 2.6 ounces ( 6.99) and have never had the shudder since then. I btw own a 95 4.6 t-bird. Hope this helps