I bought ATF DW-1 fluid for my '97 Accord automatic (F22B2). Not sure when the last time the fluid was changed (likely been over a couple years..), there was a sizable amount of stuff on the magnet and the fluid was pretty dark. After doing one change of fluid (~3qt.) the car seemed to drive very well. The next day I drive it, and it's slipping again. Not as bad as before but it's noticeable.
I've noticed that in D3 the transmission shifts just fine, but when I'm in D4 and reaching about ~45mph is when it slips. 3rd will also slip sometimes when it's in D4, this is just really odd to me. Sometimes I'll just keep the car in 3rd when I reach 45mph then move it to D4 just so it doesn't slip. Should I keep changing the fluid until it's clean (will that ruin it?) or is there another underlying cause that could help this issue? Will cleaning the shift solenoids help much? No CEL comes up at all either.

 

One drain removes about 30% of the fluid, so a second drain an refill may help. If the issue is the clutch friction discs, then a fluid change isn't the cause of a slipping transmission.

Cleaning the shift and lockup solenoids and screens may also be a good idea.

 

Sweet, thank you