I have a 2003 auto transmission, car has 155,000 miles on it now.

The transmission doesn't feel like it's slipping yet, however, when changing gears from "R" to "Drive", etc it barely shifts.. (well you can barely feel it shifting).. Also when accelerating the gears shift very softly you can barely feel it...

If I try to accelerate really hard, the car goes without any problems and no noticeable slip is detected.

It didn't used to be like that, you could feel each shift and changing gears while stopped from "R" to "D" etc you could feel the car trying to move.....

Anyone have any ideas?

I have changed the transmission fluid at 60,000 miles, 100,000, and 150,000.
with OEM transmission fluid.

 

you running any grounding wires?

My car was like that before...at 150K miles it still shifts hard.

 

Check the cold fluid level (ie let it sit overnight). Any CEL's on? MPG still consistent? Mods? Are full throttle shifts still firm?

Try disconnecting the negative battery wire for about 10 minutes, hit the brakes to discharge all energy, reconnect, and then go drive. Do that and see if the tranny becomes lively again.

 

Fluid level is okay.... No CEL's... MPG is still as good (or bad) as always, around 22 to 23 mpg...........

I had the battery disconnected for about 6 hours when replacing my valve covers recently. That didn't help any... Maybe a full ECU reset could help.

At full throttle it feels very firm, without any noticeable slippage.

But when just taking it easy, all shift points are very soft, if it weren't for the RPM changes during shifting I would never know or feel that the transmission is/has shifted.

 

Is your rpm different than what it used to be at cruising? Maybe torque converter lockup?

 

Check your motor mounts

 

Yeah try thefull ecu flash