So I have an 05 TL auto which slipped once going from 3rd to 4th I put some more trans fluid in it along with a stop slip thing and it hasn't slipped again. It does make a pretty noticeable torque convertor whine but only on startup, once it warms up the noise goes away completely, should I just do a fluid flush and hope that it fixes the problem. Does anyone have any experience with this problem?

 

Stop slip stuff can make a lot of problems esp when cold as it's very thick.

Drain that crap out and use proper fluid. Replace the 3rd and 4th gear switch and also replace the filter on the side of the trans. 04-06 models have this filter that can be replaced.

 

Slipped once, did it?

 

whats the proper drain method isnt it drain all and put 3 quarts in drive a bit and then drain and then put in 3 more quarts and you are good to go?

 

We call it a 3X3--do the 3 quarts 3 times.
Check your fluid level after the third fill--you may need to add about a 1/4 quart. Check your dipstick level.
You should also use a new crush washer on the drain bolt to minimize chance of leaking.
Your 05 has an external trans fluid filter just below the engine fuse box that should be changed--most people skip it.